"It is not the perfect picture we are looking for, but rather time spent to be captured." -Aanestad
Before he met Ash, his only friend was his camera. He likes to take shots of Pokemon in the wild, happy in their native habitat. But from Ash he learns to better understand and appreciate Pokemon. He travels with Ash for a few episodes.
Snap and Ash met when Team Rocket hired Snap to 'capture' Pikachu. They'd read that he was famous for capturing Pokemon. Unfortunately, they didn't realise his talent was capturing them... on film. So Snap followed Ash around, trying to take a good photo of Pikachu.
In the end, Team Rocket got fed up and attacked them both. Snap saved Ash's life, securing a friendship between the two, where before, there was some hostility. (Snap was a little rude to Ash. Their initial meeting was where Ash saw his shutter in the bushes and thought someone was trying to shoot them. ^_^;;)
While Snap can be a little arrogant about his photography abilities, he's mostly fairly nice. He took the only known photo of an Aerodactyl, and his snapshotting is his main character point; he takes a shot of Ash looking stupid, he takes photos to prove Butch and Cassidy are mistreating Pokemon, he takes photos to MEET Ash, etcetera.
Snap left the group to take more Pokemon pictures. Naturally.
He is also the star of a game of the same name: Pokemon Snap. In that game, you play the role of Snap, going around different terrains and taking photos of the Pokemon there to show Professor Oak, your employer-of-the-moment.
Snap's voice sample - click here to hear what he sounds like. "My name's Snap, and I love taking pictures." (Crappy sound quality, btw.)