In film series, he is voiced by Jonah Hill.
In TV series, he is voiced by Zack Pearlman.
How to Train Your Dragon
Snotlout is rumored to still be Hiccup's cousin, but he definitely doesn't treat Hiccup that way. While this idea came from the book, they're more like rivals rather than relatives of the family. Throughout the movie series, he has an obvious crush on Astrid. He tries on several occasions to flirt with her through various means, such as by "impressing" her with his strength or "ability to block out the sun", though he fails each time. When Hiccup teaches the Viking youths how to befriend Dragons, Snotlout seems to be the only one who is actually afraid, reaching for a spearhead before Astrid discourages him. Under Hiccup's tutelage, he successfully befriends a Monstrous Nightmare, which he flies during the battle with the Red Death, though he is knocked off and forced to attack its eyes head on (and is somewhat successful).
Although he would often taunt Hiccup over his lack of skill, he never seemed to hold the same level of dislike for him that he did in the books. When Hiccup starts doing well in Dragon Training, Snotlout quickly joins the ranks of his adoring fans. When Hiccup is shown to have survived his encounter with the Red Death, Snotlout actually sheds a tear in relief.
How to Train Your Dragon 2
In this movie, Snotlout has apparently given up on Astrid, as she is officially with Hiccup, and started to hit on Ruffnut along with, for some weird reason, Fishlegs. He has grown up, looking more like his father, and seems to be a bit less arrogant and obnoxious.