From the Super Mario Wiki
“My love for Bombette is deep like the southern sea! Bomb! Even being dumped constantly won't discourage me! Ba-bomb!”
Bruce is a blue Bob-omb from the game Paper Mario. Though he was initially found locked up in Koopa Bros. Fortress, he later moved into Koopa Village and took residence in Kooper's house with two friends.
As stated above, Bruce is first encountered alongside several other friendly Bob-ombs in the prison cell of Koopa Bros. Fortress, where Mario first meets Bombette. Like all other Bob-ombs featured in Paper Mario, Bruce is thought to have once resided peacefully in Koopa Bros. Fortress (and even coexisted with the Koopa Bros. convivially for some time), although his calm life was disrupted when the Koopa Bros., tainted by Kammy Koopa's favor of them, began working him and the other Bob-ombs as slaves, displeasing them. Soon, Bob-ombs such as Bruce and his companions began to revolt on the Koopa Bros., which resulted in them being locked up in the prison room Mario met Bruce in. Using Bombette, Mario eventually allowed Bruce and the other Bob-ombs (as well as his own party) to escape Koopa Bros. Fortress. Afterwords, Bruce, as aforementioned, moved into Kooper's unused house in Koopa Village.
Bruce seems madly in love with Bombette, although their one past relationship would appear to have ended unsuccessfully due to Bombette's inability to return his love. Despite this, though, Bruce continues to love Bombette to an obsessive point, which seems to simply annoy Bombette and the other Bob-ombs.
Bruce is very minor to Paper Mario and plays no exceptionally large role, though he does play a part in one of Koopa Koot's Favors, which involves Mario having to keep him from exploding as to earn three Star Pieces from Koopa Koot. He also writes two love letters to Bombette through the Post Office.