The Robo-Buster was a robot invented by a man named Paul Smart to replace the Ghostbusters. Paul created the robot by stealing a trap containing a recently-captured ghost and photographing blueprints for the PKE Meter and proton pack. The Robo-Buster can fly and has proton cannons built in its arms. The thing about it that seemingly made it better than the Ghostbusters is that its proton streams not only caught ghosts, it also completely destroyed them if they were in the streams long enough. Because of this, the Robo-Buster did not need a trap or a Containment Unit. In actually, it was disassembleming their essesense, which later recombined themselves into one giant ectoplasmic gestalt. It appeared in Robo-Buster.
Being a robot, Robo-Buster didn't have much in the way of a personality. While it will address the ghosts before it "destroys" them, this is more likely a pre-programmed response. In it's commercial it proclaims "I am not afraid of any ghosts!". However this is also likely to be programming as well, and not indicative of a personality. At best Robo-Buster is simply an automaton, more equipment than character.