Ash's Butterfree (Master)

Ash's Butterfree was the first Pokémon caught by Ash Ketchum in the Kanto region, and his second overall.

Kanto
Butterfree, as a Caterpie, was found by Ash and Ash decided to capture it. Ash used Pikachu to battle it, and then Ash captured it. Immediately upon being captured, Caterpie had likened Ash and Pikachu, also Misty though Misty disliked the bug-type.

Caterpie was then used to battle and capture a Pidgeotto despite the type-disadvantage, though Ash returned Caterpie. Caterpie evolved soon after, into a Metapod. Ash later battled a Samurai's Metapod with his own Metapod, and the battle ended as a stalemate. A horde of Beedrill soon chased after them, and Metapod evolved into Butterfree and used confusion to defeat them all.

Ash used Butterfree in his gym battle against Brock, originally using it to battle Brock's Onix. Onix overpowered Butterfree, and Butterfree fainted. Butterfree later battled Brock's Geodude and defeated it with ease, before poisoning Onix and then being returned.

Butterfree was later used to battle Misty's Staryu, and defeated Staryu.

Sometime before reaching Saffron City, Ash encountered a Butterfree mating area where Butterfree would mate and then fly away with its new mate. Ash bought Butterfree a yellow scarf to impress another pink Butterfree, and failed but then the pink Butterfree decided to mate with Ash's Butterfree after he had stopped the Team Rocket Trio from kidnapping them.

Personality and characteristics
As a Caterpie, he had a shy but kind attitude and made friends with everyone easily. He had low self esteem issues, as seen when Misty disliked him and when the pink Butterfree rejected him. Upon evolving into Metapod, Metapod had become notably lazier but was willing to protect Ash from a horde of Beedrill. As a Butterfree, he remained similar to his personality as a Caterpie but was more positive and brave compared to before. His self esteem issues stopped as he was released and Ash told him he was proud.