General Nathan was an American army general who appeared in the episode Get Schwifty. He wanted to destroy the Cromulons with nuclear weapons, but the President disagreed. He rebelled against the President and knocked him out, only for his plan to destroy them to fail. He is killed by Rick's particle beam wristwatch when he attempts to murder the President.
General Nathan's overall appearance, way of speaking and manner is likely a reference to Gen. Buck Turgidson, a similar military character played by George C. Scott in the movie "Dr. Strangelove."