Geno is a playable character from Super Mario RPG. He was awesome. Originally a lifeless doll like Pinocchio, a spirit from Star Road inhabits the doll and calls himself Geno. He joins Mario's party in the fight to recover the stars and defeat the evil Smithy. Geno was a fan favorite (Actually, all the SMRPG characters had fans) mostly because of his effectiveness in battle. He utilized multi colored lasers, even turning himself into a big cannon in one attack.
Unfortunately, because Super Mario RPG was made by Squaresoft (Now Square-Enix), the Geno trademark does not belong to Nintendo. However, Nintendo did manage to work out a deal to have Geno make a cameo in Mario and Luigi: Superstar Saga as a tutorial instructor for a minigame.