Goombario is a Goomba that first appeared in the game Paper Mario for the Nintendo 64. In the game, his grandpa, Goompa, explains that they named him after Mario. When Mario goes into the Goomba village, they treat him nice, and Goombario ends up joining Mario's party.
In Paper Mario: The Thousand-Year Door', Goombella fulfills the same role as Goombario did in the original Paper Mario. In addition, a hacker managed to find sprites of Goombario in Paper Mario: The Thousand-Year Door, meaning Goombario was planned to be in the game.