Bob, AKA (Bobblen, Bobblun and Bobbaloon) is a Bubble Dragon, and the younger brother of Bub, and has always assisted him on 95% of his adventures throughout the years in Rainbow World, with the few exceptions due to being unwell etc.
Several times throughout the Bubble Bobble series, Bobblen has been too unwell to help Bub in his adventures. Most notable are Bubble Bobble Pocket and Classic Bubble Bobble. Both of these games, it is down to Bub to go on a quest by himself to help Bob get well again.