He's the person that's the reason the game is named Bob's Game.
He has special features such as:
The BLJ is a trick used by many SM64 speedrunners to build up speed and pass through otherwise unreachable places. By pressing U and using the movement keys (WASD, or ←↑→↓) you can double your speed!
His weaknesses are:
Bob doesn't particularly enjoy water on his clothes so going in water will lose you 5 coins for cleaning.
Bob is shorter than Luigi, so attempting to get onto a high spot won't work unless he has a ladder.