The fact that Draco Malfoy is canonically unable to cast a Patronus because he doesn’t have a happy enough memory to use for it is a MAJOR detail. He may be spoiled and doted on at home, and his mom clearly would do anything for him, but any kid with NO memories happy enough to conjure a Patronus whatsoever, is definitely not a kid with parents who are 100% warm and loving. I think this is a big reason why Lucius being full-on abusive is a common trope in fanfiction. There’s plenty of stuff in canon to contradict that - and yet Draco’s lack of Patronus isn’t exactly a point in Lucius’, or Narcissa’s, favor.
We don't talk enough about how the only reason why it took Harry an entire year to learn the patronus charm was because whenever Harry was near the boggart-dementor he hear his parent's voices, and at that point that's the only time Harry ever heard them speak.
The only reason why Harry was able to push past that and drive the dementors away (hence driving his parent's voices away) was because Sirius was in danger. Sirius, who wasn't his parents, but was the closest thing, the only living family Harry had left. The desperation to keep Sirius outweighed Harry's desire to keep on listening to his dead parent's and he finally managed to cast the charm.
Okay, it took me some time to answer this ask since I needed to spend some time thinking. I didn't really have an answer in mind until your question. It's just something I apparently never thought about. So I was interested in finding the most canon-adjacent answer I can for if Tom Riddle/Voldemort could cast a patronus, what would it be.
So, my approach to finding the right animal was based on a few factors, the first of which:
How exactly is the form your Patronus takes determined?
Because we don't actually get a straight answer in the books. We know Patroni can change with a person, but we don't exactly get an answer on what their form represents and why some couples have matching Patroni.
Basically, I don't know what you expected, Anon, but what you're getting is some rambling about the magical theory behind the Patronus charm followed by why that means Tom gets a certain animal over another.
So, let's start with the basics, the incantation:
"Expecto Patronum"
This is in Latin and literally translates to: "I await/expect a defender"
And Remus Lupin explains what the Patronus charm is as:
“Well, when it works correctly, it conjures up a Patronus,” said Lupin, “which is a kind of anti-dementor — a guardian that acts as a shield between you and the dementor.”
...
“The Patronus is a kind of positive force, a projection of the very things that the dementor feeds upon — hope, happiness, the desire to survive — but it cannot feel despair, as real humans can, so the dementors can’t hurt it. But I must warn you, Harry, that the charm might be too advanced for you. Many qualified wizards have difficulty with it.”
(POA, page 237)
We also know the patronus is cast by thinking of a happy memory — well, not really. The memory isn't really important; the emotion is. The memory is to help you have the right happy feelings that can fuel a Patronus. "You got to mean it" just like with an unforgivable.
So, what does it tell us about the Patronus:
We have a defender made out of happiness, literally.
This already sounds like something Tom Riddle would struggle with. I don't really see canon Tom Riddle/Voldemort being capable of producing one, but let's assume he can in some hypothetical AU. Let's take a look at a few patroni to see how their form is chosen and why.
Obviously, we have Harry's (and James') stag. A stag symbolizes many things in different cultures, but deer (both Stags and Does, like Lily and Snape) in general symbolize:
The cycle of life and death
Agility and grace
Bravery
Nobility
All this fits the Potters quite well. The nobility and bravery of Gryffindor and the cycle between life and death. Stags actually represent regeneration, as in a return from death, which fits with the Potters' connection to the Paverells and death perfectly.
Stags also symbolize authority, strength, leadership, and fatherhood, while does symbolize femininity, grace, intuition, and devotion. All in all, both animals fit James and Lily well. And while the stag does fit Harry (to a degree), I don't think his Patronus represents him.
I think Harry's patronus is a stag because James' patronus was a stag. Harry was actually convinced his father cast the Patronus when he first saw it in POA. And it makes sense.
I don't remember where I saw this theory, but it essentially was that your patrons would represent a person or an idea that you feel will defend you. It's why certain couples have matching Patroni, why a Patronus can change when you or your feelings about people change.
And Harry, when he casts his Patronus, the idea of his father who he never knew but would have protected him is the idea represented in Harry's Patronus. It's a stag like James' not because Harry and James are so similar (they have very different personalities actually) but because Harry's Patronus is James. It's a stag because James was a stag, and Harry is calling the concept of his father to defend him.
Following this logic, Lily's Patronus is a doe, because she is the doe. Lily's defender is herself. Courageous, noble, graceful and devoted. Lily's devotion to her son is what literally sets the series into motion. The reason she and James match is that they always have. He was always represented by the stag and she was always represented by the doe. Their Patroni aren't matching because of their relationship with each other, but because they are so compatible their Patroni matched from the get-go.
Snape's Patronus is a doe because of Lily. Lily is represented by the doe. As she was Snape's first friend and defender, whenever he calls for a protector, it's Lily.
Let's look at a few other Patroni, like Hermione's otter:
Playfulness
Joy
Family and close-knit friendships
Loyalty
All of this doesn't really sound like Hermione. Ron's Jack Russell Terrier on the other hand:
Loyalty
Courage
Playfulness
Cleverness
Protectiveness
Tanasity
Does sound very in line with who Ron is.
But then who does Hermione's otter represent? Well, an otter is from the weasel family and the list of characteristics looks closer to Ron's list of traits than Hermione's. I think Hermione's otter represents Ron who did step in to defend her since the troll incident in their first year multiple times.
So, where does that leave Tom Riddle?
Well, we established the Patronus becomes your defender, and in Tom's case, it'll be himself. Tom is distrustful and sees himself as more capable than anyone else. Not to mention he never had a real connection or person in his life he could call upon to defend him. So, whatever animal his Patronus is would represent himself as his own defender.
So, which animal represents Tom best?
The first animal I thought of, is of course: the serpent. Snakes are heavily associated with Tom (for obvious reasons) and is an animal we know he has a soft spot for. When looking at what snakes represent, you can see why he is associated with them:
Deceit
Transformation
Power
Regeneration and rebirth (shedding their skin)
Healing (Cadcadeus)
For the most part, the list seems to fit him well. Specifically their association with rebirth and the cycle of life and death by shedding their skin. Deceit and power are also right up Tom's alley. And even transformation considering he rewrote his entire identity to become Voldemort.
But, just "snake" wasn't good enough for me, I wanted to know which kind. And as I wanted his Patronus to be as rare as Harry's stag, I went to the list of official Pottermore possible Patroni to find a snake that is as hard to get in the test as the stag while not being magical.
(Magical Patroni are incredibly rare and to have yourself represented by a magical creature in your Patronus you need to be incredibly unique or incredibly full of yourself. At least, that's how I see it)
And low and behold, there was one on the aforementioned list:
The King Cobra
So I looked up if this snake has any interesting additional unique symbolism that would fit Tom. And, well, there was:
Authority and Leadership
Aggression and Fearlessness
Destruction and Creation
Intelligence and Cunning
Which all in all sounds fitting for Tom Riddle.
I also continued reading and apparently, snakes are associated with lightning by some Native American tribes. And when I saw that I was sold on the idea. Considering how the killing curse is represented by lightning (Harry's scar and the lightning-struck tower being the name of the chapter Dumbledore dies in). It feels appropriate with Tom's connection with snakes.
The King Cobra is actually not really a Cobra and is considered a unique breed of snake, which Tom would approve of. It's also the longest venomous snake and its venom can result in a rapid fatality, as soon as 30 minutes following a bite. It's also a cannibal snake that eats other snakes, including its own kind.
Overall it just fits perfectly, both in traits, symbolism, and how rare and dangerous it is. So, for your question, I think Tom Riddle's Patronus, if he could cast one, would be a King Cobra.
We see it said multiple times in the books that the Charm is a direct reflection of the caster, but it's pretty clear that this isn't true. Tonks's Patronus is a wolf, and stated to be an expression of her love for Lupin. Harry's stag is pretty often seen as confermation of his resemblance to his father. Which I would say isn't the whole of his being. Snape's doe is also not reflectent of his person.
So, I have come to the conclusion that your Patronus can either reflect your self. Or something else. (Btw, I don't think the whole true love thing Rowling talked about is the case)
Is the Patronus a reflection of the caster? That's Lily's doe, James's stag (we don't know if he could produce one), Dumbledore's Phoenix, Lupin's wolf, Arthur Weasley's weasel, Ron's dog, Aberforth Dumbledore's goat, Luna's hare, McGonagall's cat, and probably Kingsley's lynx
Now the other thing is more complicated. We don't actually know all the characters with the other type of Patronus that well so we can't really rule alot of causes out. Ergo I think we have to lok at everyoune individually.
Harry's stag is most likely conected to his father, since it's the same as his Animagus Form. How it is conected isn't so clear though. I'll write another post on Harry specifically.
Snape's doe is very obviously supposed to be a declaration of love, but is this actually the case — or is it just an obsession. Maybe that's just me being biased torwards Snape though (I don't like him much)
Umbridge with her cat Patronus is a very weird case. I wouldn't say she has a cats personality but I also don't think she's capable of loving anyone but herself, so I wasn't sure in which category she belongs. Maybe she wants to be seen as cat-like.
Tonks's wolf is, as previouly mentioned, thought to be an expression of her love for Lupin. I don't personally think this is true, because I feel like, what she feels is more desire for him rather than love. (remember Tonks fell for Lupin within a month and then she continued on to harras him about it for a year until he agreed to date her)
What do all these cases have in common? That they have something to do with desire specifically. Harry desires for his father to be alive therfore his Patronus is his father's Animagus. I'm sure we all know that Snape desired Lily in some way or another. I think Umbridge might desire to be like someone with a cat Patronus, even if just unconsciously. Tonks desires to date Lupin.
Following this logic your Patronus is either an extension of yourself or the person (or personality) you desire.
This amazing art by @giselsann-opencommissions I'm so excited to continue getting art for this series! If you've read it let me know which scenes you'd like to see! :)
Here's some excerpts from this chapter!
“Expecto Patronum,” Sebastian murmurs the incantation and something bursts from his wand. A few people gasp as a massive three headed snake, probably six feet long, slithers across the floor.
“A Runespoor,” Hermione informs the class as people whisper and point at it. "They’re a magical beast that is native to Africa. Each head has a unique purpose. They’re incredibly rare.”
Sebastian’s face is filled with open wonder. Evie watches him admire the creature as others step out of its way as it moves gracefully around the room. Despite the creature being a deadly one, it’s rather peaceful to watch it.
“Sebastian, it took me weeks to produce a corporal one,” Harry informs him with an amazed grin. “You did it within a few minutes!”
“I’m an overachiever,” Sebastian shrugs but his eyes tell a different story. He’s amazed he was able to produce one. Evie did a little research in the library on her own after he told her about them and learned that dark wizards can’t normally cast the charm. After what happened last year with Solomon she knew that he worried about it. But he's not a dark wizard, he's good. She’s very proud that he did it, proud of him. Sebastian is wonderful in so many ways. He deserves to shine.
With her wand held steady and that warm feeling in her chest Evie casts the charm. “Expecto Patronum!”
Blinding silver light has some of the other students staggering back, someone even falls backwards onto their butt.
“Merlin’s beard!” One of the Weasley twins exclaim and Evie looks upon her patronus with a strong sense of pride. An almost familiar looking dragon flies around the room, wings fully extending, casting silver light across every single persons stunned expressions. Her Patronus is a dragon.
“That’s a Hebridean Black!” A Hufflepuff boy Evie doesn’t know the name of stares open mouthed at the massive patronus. It dwarfs all the others in the room. There’s a wave of power emanating from it. Evie can feel it warming her soul.
Sebastian tilts his head the side, a pleased smile appearing across his lips as he looks at her. He's the only person in the room not staring at the Patronus. He's looking at her and Evie feels his gaze in every part of her body. “One of the most aggressive creatures in Britain,” he points out. “And the most beautiful. Fitting for you, darling.”
