The man who would became Doctor Sun was born in People's Republic of China, and became an important scientist working for the state. He was the mind behind Project Mind, aiming to separate a human brain from the rest of the body, and then linking it to a computer.
During the Great Proletarian Cultural Revolution of China in 1966, Sun became an enemy of a Chinese general who obtained power and support from the new government. The general accused Sun of perceived stalling of the Project, arrested him and sentenced him to death. With irony, he decided that Sun would became a test subject for his own project. A group of doctors (amingst the Sn's son) stopped Sun's heart, took his brain out with surgery (but without anesthesics) before it would suffer cell deterioration, placed it in a jar where it would receive oxygen and feeding, and then joined it to a computer network.
Sun's brain could now access the electric energy on the computers, and attacked the doctors with psyonic rays. Sun discovered that he had obtained great powers, partly due to his knowledge of the project (It is unclear if a different person would have obtained the powers; it is unclear if there was an accident somewhere or if Sun's goal was this from the very beginning).
Sun had some mind control powers, and so he enslaved a number of people, who would hide Sun's activities to the Chinese authorities.
Sun also discovered that his brain needed constant supplies of fresh human blood to survive. He decided then to study Vampires, who also fed on blood.
After a time, Sun decided to leave China, looking for revenge and world domination. Sun's studies suggested that vampires could be the perfect soldiers for him, and he wanted to control all of them to use them as an army, and to provide him with blood.
Sun managed to get hold of a vampire agent, Lucas Brand, and trained him to fight the most powerful vampire on Earth and lord of all the other vampires, Dracula.
Sun managed to capture Dracula and tried to transfer Dracula's memories to Brand's brain, so that Brand could control the vampires. However, Brand was defeated by Dracula, who still retained his memories, and then Dracula fought Sun. Brand then rebelled against Sun, siding with Dracula. Sun killed Brand but both Sun and Dracula survived, marking the beginning of the rivality between them.
Unbeknowst to Dracula, Sun had initiated a proccess to transfer Dracula's powers to himself. He needed a specific machine to do so, and thus he decided to run away as time would be on his side.
After unsuccessfully trying to acquire a statue of the Chimera from David Eshcol's father and clashing with Dracula once more, Sun moved to Boston, Massachusetts, and hired a new minion, Juno, a man who had a silver lance instead of left hand. In Boston, Sun had Dracula's enemies Frank Drake, Quincy Harker and Rachel van Helsing brought to him by Juno. Harker discovered the machine Sun was using to get Dracula's powers, and destroyed it, stopping the transfer (although Sun still retained the previously drained power).
Finally, Dracula was brought to Sun by Juno as well, but the vampire lord was weakened. Dracula fought Juno and was defeated and stabbed. Sun incinerated Dracula's body so he would not be accidentally resurrected. However, once this was accomplished, he allowed Drake and his companions to go. Sun thought Drake would came back with soldiers to fight him, which was exactly what he wanted.
Precisely, when the soldiers came, Sun used Dracula's hypnotic powers, increased with technology, to control the minds of the soldiers. He had created a core for his army, which would increase with the same method.
Drake and van Helsing found an ally in writer Harold H. Harold. The three of them raided Sun's base to recover Dracula's ashes: They had to resurrect him to fight Sun, a greater threat. When resurrected, Dracula recover all of his powers at the maximum level, although Sun did not lose them.
Dracula looked for Sun and fought him again. Accidentally, Sun destroyed his own computers and the case containing his brain, declaring a fire. Drake, Dracula and other witnesses saw a brain burning in the fire, and all of them believed it was Sun's. However, Sun had beheaded Juno and leave Juno's brain visible so that they would believe him dead. He then teleported his real brain to a different base. In this new base, Sun built a new robotic body to host his brain. Afterwards, Sun found superheroe Nova and discovered his secret identity as student Richard Rider. Further research made Sun discover Nova's relationship with Nova Prime, a xandarian starship orbiting Earth. Sun captured Nova and threatened him so that both of them could be teleported to the ship. Sun aimed to use the computers in the ship to take over the world. He also tried to form an alliance with Diamondhead, Nova's enemy, but Diamondhead was not interested.
Then, super-villain Sphinx appeared, took control of the ship and took it to planet Xandar. Sun escaped from the ship reaching the planet, where he would project his consciousness to the computer network of Xandar. The Fantastic Four went to Xandar and became friends with the Xandarians, who acceeded to a hyperlink between their computers and HERBIE, a robot created by Mister Fantastic. Sun then transfered his consciousness to HERBIE and went back to Earth with the Fantastic Four. He found he had much more mobility than before, as well as a chance to kill the Fantastic Four and then steal the Sphinx's power.
For a time, Sun remained dormant (or sorts) in the robot body, acting only from time to time. During a stop in their trip back to Earth, the Fantastic Four fought some spider-like aliens, and one of them sneaked into the ship. Sun killed the alien, but then feigned ignorance, saying he was not programmed to end a life. He also went with the Fantastic Four to recruit Terrax as a herald of Galactus, but Terrax attacked the Fantastic Four and then Sun sneaked away, trying to prepare a plan.
Sun accepted Reed Richards' orders to take the Thing's body to Baxter Building while the Fantastic Four fought the Sphinx, until the Sphinx was defeated.
But then, Sun began his own plan to destroy the Fantastic Four. He firstly released Blastaar from the Negative Zone. However, Blastaar was defeated. Sun attacked the Fantastic Four himself. He defeated Reed Richards and the Thing with HERBIE's weapons, and the Invisible Woman and the Human Torch with weapon systems of the Baxter Building controlled through HERBIE.
Sun then transfered his consciousness to the main computer of the building; he wanted to use all of the weapon systems in the Baxter Building to destroy the Fantastic Four. However, Reed Richards sealed the main computer from any other system, using his pliable body. Thus, Sun was trapped: He could stay in that particular computer or go to HERBIE, but nothing else.
HERBIE, who had been programmed to avoid damage to the Fantastic Four if he could avoid it, understood that Sun could possess him again and attack the Fantastic Four. Heroically, HERBIE charged on the computer, destroying it (and himself) in the proccess. Apparently, Sun's consciousness stopped existing from that moment onwards.