R.O.B.

History:

R.O.B. the robot is an interesting case. Scholars in the Mushroom Kingdom are unsure of where exactly he came from but sources indicate that it is possible that he is a temporarily displaced in his own space-time, similar to how Master Hand is able to assemble fighters for the Super Smash Tournaments. R.O.B. does not originate from the Mushroom Dimension and so has no real ties or relationships to anyone else. He exists only to race, although he had some kind of natural connection to Rainbow Road, perhaps using his temporal displacement to help construct the similarly otherwordly track.

DS:

R.O.B. appears only as an unlockable character in DS for some reason. He really has no purpose being here but nevertheless he provides another good heavyweight character. The system in DS provides three unlockable signature Karts for each character, although every character may use any Kart. These include a standard, one with better stats but a weak Item rating and one with worse stats but a high Item rating. R.O.B. generally has excellent Speed, along with the best Acceleration and Handling of any Heavyweight. He is also tied with Bowser as the Heaviest driver, adding 3.5 to the weight of each Vehicle. This all comes at the expense, however, of his Drift, which is the worst in the game. Take a look:

There are also Staff Ghosts in DS. R.O.B. owns the Desert Hills track for some reason, with a time of 1:31:262 using the ROB.-LGS along with Rainbow Road in the ROB-BLS in 2:16:246. The Rainbow Road here makes sense, R.O.B. is a weird character for that weird track, but the Desert Hills is awfully random. Needless to say, R.O.B. did not make a comeback after this game.