Let us appreciate His design.
Referring to my previous post, it's very obvious the main (and may I say, coolest) design element of Herobrine comes from white eyes. Now, that itself comes for a glitch, which is perfect for Him. Notch's dead brother actually originates from a glitch? Hell yeah. (Or rather, Nether yeah if we're feeling funky.)
Aside from that, we have the basic modification of the Steve model. I've seen someone mention the clones you could spawn in older versions of alpha that would jump around with their arms flailing around and it's a pretty neat idea that maybe Hero was once a silly little clone NPC jumping around before being possessed. Obviously, not how his story goes but I do think it's funny to me, so you should live with that image in your head.
Let's start off with the "cannon" version, as cited by the Wiki.
It's pretty simple and just Steve edited with white eyes. Nothing too crazy, but there is a beauty in such simplicity. The potentials for horror are, very obviously, vast and iconic.
Today, most versions of Herobrine you see around will have a beard, which I think is a nice little distinction from Steve. If you look closer, the pixel art on their hair is also laid out differently, and I just think it's neat. (It might just be the author of the texture going crazy though.) However, it should be made clear that while the more popular and widely accepted version of Him does have a beard, once again, it is not cannon.
The image below shows the "fanon" Herobrine compared to Steve.
I personally prefer the bearded version as it does separate Him from Steve, but when talking about the original it's worth pointing out that it might not even matter. And in truth, it doesn't. It's just something I found interesting while researching Him.
And to go even further; have you seen those different skins of Him people have made? I mean come on. They are awesome. My inner 10yo is giggling in glee.
I do truly appreciate how much diversity the simple white eyes have opened. Don't get me started. I could rave on for days.