From the Super Mario Wiki
Kooper is Mario's second party member in Paper Mario. He is a blue, adventure-loving (and seemingly young) Koopa who dreams of becoming an archaeologist like his childhood hero Kolorado. He is the exact opposite of his successor, Koops, personality-wise. However, in the battle field, the two have very similar abilities. Kooper's name is a pun on "Cooper", but with a K for Koopa.
In Super Paper Mario, Kooper appears as a Catch Card found on the thirteenth floor of the Flopside Pit of 100 Trials. In Super Smash Bros. Brawl he is a Sticker that raises arm attack power of a player by ten.
Mario and Goombario enter Koopa Village to find that Fuzzies have attacked the village and are stealing all the Koopas' shells. Mario gets the shells back for the Koopas and eventually finds Kooper. He tells Mario that his blue shell had been stolen by a Fuzzy and Mario agrees to get it back. Once Mario gets the shell back for Kooper, he joins the party. In the field, Kooper will retreat into his shell and Mario can shoot him out short distances, allowing him to flip switches, grab items and attack enemies.
When the game ends, Kooper is seen in an expedition with Kolorado in Shiver City. Kooper is told by Parakarry that Peach wants him at the party (which is held at the end of the game). Kooper wants to help Kolorado instead, but Kolorado insists he goes to the party, and so he does.
Paper Mario: The Thousand-Year Door
Although Kooper himself doesn't appear in Paper Mario: The Thousand-Year Door, early concept artwork exists and unused sprites are found in the game's coding. Additionally, he was replaced by Koops in the game.
Super Paper Mario
Although Kooper doesn't appear in Super Paper Mario, his sprites are still present in the game's coding.
Kooper also appears as a Catch Card.
Card Type: Rare
Names in other languages