From the Super Mario Wiki
Franky is a Boo in the game Paper Mario. An inhabitant of Boo's Mansion, Franky first appears after Lady Bow, the mistress of the mansion whom Franky has a crush on, joins Marios party. Aside from mentioning his affection for Bow, Franky offers no real advice to Mario.
In a sidequest involving delivering letters, Mario and Parakarry can deliver a letter to Franky from Little Mouser, the owner of the shop in Dry Dry Outpost. After receiving his letter, Franky will give Mario and Parakarry another one to be delivered to Dane T. of Toad Town, the letter being an invitation inviting Dane T. and his friends to Boo's Mansion.
One of the favors Koopa Koot involves asking for an old photograph depicting a younger Koopa Koot that Franky possesses. Before giving Mario the photo, Franky will tell him that it was taken when Koopa Koot passed through the area, also stating that Koopa Koot has a habit of manipulating people.