Doctor Sun was a robot controlled by a living brain whose hunger for power brought him to download his consciousness into the Xandarians' computer systems. He desired the power that the being known as the Sphinx represented, who fought with the Xandarian Champions and the Fantastic Four. When Mister Fantastic created the robot H.E.R.B.I.E., based on a cartoon show’s character, Doctor Sun downloaded himself into the robot to increase his mobility and try to steal the power of the Sphinx.

While the Fantastic Four used H.E.R.B.I.E. to pilot the Nova Prime ship they were given by the Xandarians, Doctor Sun remained relatively dormant within the robot’s body. Though Sun acted on his own accord when a spider-alien attacked the Nova Prime ship while the Fantastic Four were away, fighting more of the spiders. Doctor Sun killed the alien, but as H.E.R.B.I.E., he feigned ignorance when the four returned, explaining that he wasn’t programmed to end anyone’s life. He later went along with the Fantastic Four when they were sent to recruit Terrax the Tamer for Galactus’ herald, but once Terrax’s master left to fight the Sphinx and Terrax disobeyed him to attack the Fantastic Four, Doctor Sun snuck off to further his own plans.

Doctor Sun’s plans were soon interrupted, as Reed Richards needed H.E.R.B.I.E. to carry the Thing’s aging body back to the Baxter Building. He did so, and once Ben and the Invisible Woman were safely in stasis, Doctor Sun flew off to restart his plans. After the defeat of the Sphinx Doctor Sun used H.E.R.B.I.E. to release Blastaar from the Negative Zone to destroy the Fantastic Four. Blastaar failed, and Doctor Sun was forced to take action himself and attack the four directly. As H.E.R.B.I.E., he disabled three of them and soon downloaded his consciousness into the Baxter Building’s main computer to trap the Human Torch.

While he was disconnected from H.E.R.B.I.E., Reed used his own pliable body to stop Doctor Sun from taking over the computer and freed his team members. With H.E.R.B.I.E. being the only avenue left for him to escape into, the Reed’s robot reasserted his original program and bravely threw itself into the main computer to save the Fantastic Four and destroy the consciousness of Doctor Sun.