Doctor Sun was a robot with a living brain and a hunger for power who downloaded himself into the newly created robot H.E.R.B.I.E., where he lay mostly dormant in an attempt to steal the power of the Sphinx. He went along with the Fantastic Four and pretended to be their obedient servant, but secretly he crafted his plans when unobserved.
After failing to kill the FF by releasing Blastaar from the Negative Zone, Sun was forced to directly attack the four starting with the Invisible Woman. Once he had subdued most of them he uploaded himself into the Baxter Building's computers to gain more power. But Mister Fantastic recovered from his attack and shut down the computers to stop him. Sun's last avenue was the body of H.E.R.B.I.E., but the newly freed robot sacrificed himself by rocketing into the building's computers to destroy himself along with the consciousness of Doctor Sun.
