Mario has had many partners during all his adventures, all of whom help him during many points of time. Mario and his partners as a group are generally referred to as a party, as the event of a character joining is referred to as said character "joining your party." Luigi also gets partners in Paper Mario: The Thousand-Year Door, though the player cannot play as them, for Luigi is not a playable character in the game.
Mario & Luigi series characters
Paper Mario partners
Paper Mario: The Thousand-Year Door partners
Super Luigi series partners
Super Paper Mario partners
Paper Mario: Sticker Star partners