He's a background character, alive through the entirety of the first arc and the beginning of the second one. We never see him there, though, his first appearance being in Tallstar's Revenge. He's one of Mistmouse's and Hareflight's kits, along with his two sisters - Ryestalk and Doespring. He had Cloudrunner as a mentor, who later goes and becomes Morningflower's mate, who is Stagleap's daughter... That's... A questionable dynamic, but I guess that's just the norm in warrior cats at this point.
Stagleap himself is a bit of a silly playful guy, racing and playing around with other cats his age. He was Talltail's friend, even when Stagleap was already a warrior and Tallpaw still an apprentice. He said he will miss Talltail when he was leaving the clan, and later warmly welcomed him once he came back.
He was protective of his apprentice, Sorrelpaw, when Redtail and Tigerclaw beat her up. When Redtail approached him later at a gathering, apologizing and asking how Sorrelpaw was, he's understanding and reasonable. He seems to be more mature than he was back in Tallstar's Revenge, though he's still kind and a bit silly.
When WindClan was driven out of the forest, Stagleap was one of the few cats that stayed behind - along with his former apprentice, Sorrelshine, and her brother Pigeonflight. They are eventually forced to leave as well, though.
He also apparently had a crush on Shimmerpelt of RiverClan when he was young, which is pretty interesting. He was eager to see her during the gathering, which his sister teased him about.
It seems like he eventually got over his crush, since he later becomes Wrenflight's mate. They became the parents of a bunch of pretty well-known and relevant characters - Onestar, Ashfoot and Morningflower.
He unfortunately dies after getting bitten by a rat, after attempting to hunt some while WindClan was starving, somewhere near the beginning of The New Prophecy. He comes back later to give his son a life for strength, though.
I think I made him a pretty good mix of his parents' traits. From his mom, Mistmouse he got her stripes and her eye color. From his dad, Hareflight, he got his darker paws, ear tips and a part of his tail, along with the color of his nose, inner ears and paw pads. I'm still trying out some more dynamic poses, so I drew him in a fight - maybe with ShadowClan, maybe with the rats that had eventually killed him.
But in merrier news, I just realized that Stagleap and Doespring are siblings? That was petty cute Erins. Lovely matching names. 10/10
Everyone in that family is named after animals, actually. Except for Ryestalk, Stag and Doe's littermate. Guess she's lowkey the black sheep huh. So sorry lass 😔