Doctor Scientist is a Science Being scientist in Sparks Nevada, Marshal on Mars. He is played by Craig Cackowski in The Agony of the Feet, Samm Levine in War of the World, and very briefly by James Urbaniak in the episode introduction of Do the Fight Thing.
In The Agony of the Feet, where Sparks and Croach attempt to enlist Doctor Scientist's help, but he is not home. Sparks and Croach listen to a recording of his voice when they visit his place and ring the doorbell.
In War of the World, Doctor Scientist is drilling into the core of Mars in order to make Mars into an ultimate destructive weapon against the Science Beings war with the Technology Beings. He and Technos the Advanced eventually agree to use the planet as a staging ground for war instead of the means of war after their Science and Technology infect the planet against one another.
He is a huge fan of Rebecca Rose Rushmore, and very much wants her to bring back Bathazoid the mecha angel in the Robot Lazarus series.
It is presumed he fought in the war in Do the Fight Thing, but was not mentioned by name.