When the Goa'uld first arrived on Earth, Sokar began to align himself with the personas of various underworld demons, including the Biblical Satan. During that period, Sokar held an Unas host, though he eventually moved to a human one. For a time, Sokar was ruler of the Goa'uld, until an alliance consisting of several other System Lords, including Ra, Apophis, and Cronus, banded together to defeat Sokar. He was believed destroyed, but somehow survived. He later conquered the world of Delmak, making it his homeworld, and pyroformed its moon into a hell-like world, naming it Netu. His underling Bynarr ruled Ne'tu, traveling to Delmak by way of Rings to inform Sokar of the suffering of the damned.
In 1999, Sokar made his presence known again among the System Lords, by engaging in a war with Heru'ur while at the same time, attacking Earth when Apophis surrendered in hopes of taking the Tau'ri down with him. In order to bypass the SGC's iris, Sokar used a particle accelerator through the wormhole. After Apophis died, the SGC managed to dial out again to the planet they had found Apophis on and sent him through. Sokar ceased his attack on Earth with the Tok'ra Martouf warning that Sokar could revive Apophis with a sarcophagus. Sokar subsequently revived Apophis as Martouf predicted and imprisoned him on Netu. After learning of the death of Apophis' mate Amaunet, Sokar sent him word though Apophis did not believe Sokar. (SG1: "Serpent's Song", "Jolinar's Memories", "The Devil You Know")
On a mission, SG-1 encounters bounty hunter Aris Boch who was hunting the Tok'ra Korra to capture for Sokar. Boch press-ganged SG-1 into helping him, but agreed to let Korra go after being convinced that the Tok'ra were different from the Goa'uld. Though Boch originally intended to take Teal'c instead, he was convinced to change his mind and communicated to Sokar's ship about "technical difficulties" before he self-destructed his Tel'tak. SG-1 later learned from the Tok'ra that if Sokar had collected the bounty, he would have transported them to P3R-779, the beginning planet of the Trial of Ra rather than to the System Lords. (SG1: "Deadman Switch", "The Barque of Heaven")
SG-1 subsequently came up against an Unas in service of Sokar who pretended to be a demon on the medieval planet to get an easy source of hosts for Sokar's use. The Unas was killed by Simon and its symbiote by Colonel Jack O'Neill. On the orders of SG-1, the villagers buried the Stargate to prevent Sokar from returning for retribution with Major Samantha Carter predicting that the planet was too far away for Sokar to bother making the trip by ship. (SG1: "Demons")
Within a year of his return, Sokar was prepared to launch a massive attack against six key System Lords with a force large enough that it would guarantee him victory and rule the galaxy. The Tok'ra sent Jacob Carter/Selmak undercover in Sokar's court to discover the size of his forces. Jacob discovered that Sokar had a force ten times larger than the Tok'ra believed and was prepared to launch his attack within two weeks. However, Jacob was captured by Sokar's forces and sent to Netu before he could communicate this information.
Having learned of Jacob's capture, the Tok'ra enlisted the help of SG-1 to rescue him and learn what Jacob knew about Sokar's forces, aided by the fact that Major Samantha Carter was once the host of Jolinar of Malkshur, the only person to ever escape from Netu. On the prison moon, the team and Martouf learned from Jacob about the size of Sokar's forces and the planned attack and relayed it to Teal'c who remained in orbit in a Tel'tak. Bynarr visited Sokar to thank him for sending Jolinar's host to him to allow Bynarr to get his revenge, but Sokar realized that the people on Netu were intruders and ordered Bynarr to torture them for information then kill them, giving Bynarr one day to find out. Sokar also ordered Jumar to find the ship that brought the intruders to Netu. (SG1: "Jolinar's Memories")
After the escape of Teal'c in the Tel'tak, Jumar reported on the development to Sokar who decided to move up his plans as Sokar believed the ship to contain spies. Instead of waiting another several days, Sokar ordered that the attack be launched in two days. At the same time, having learned of the threat Sokar posed from Teal'c, the Tok'ra decided to take advantage of the fact that Sokar would take his Ha'tak into orbit of Netu to cleanse the denizens to launch an attack of their own to stop Sokar from rising to dominant power amongst the System Lords. They planned to send a weapon into Netu's core that would destabilize it, causing the moon to explode and destroy Sokar's ship in orbit.
Once the fleet was ready, Sokar took his Ha'tak into Netu's orbit as the Tok'ra predicted and called for Bynarr to report. Instead, Sokar was contacted by Apophis who had killed Bynarr and taken over Netu. Though Sokar threatened to bring the full force of his weapons to bear against Apophis, Apophis offered the information he had extracted from SG-1 and Martouf in exchange for Sokar making Apophis the lord of Netu. In reality, this was a ploy by Apophis to get close enough to Sokar to assassinate him and take his place. Sokar agreed to Apophis' request and Apophis boarded the ship through the ring transporter as Aldwin of the Tok'ra launched the weapon into the moon's core once Sokar's ship was in position. Brought before Sokar, Apophis revealed that the Tok'ra were based on Entac, a fact that Apophis had learned from Martouf. However, Sokar had recently conquered the planet and knew the Tok'ra were not located there and ordered Apophis tortured to death.
As Sokar enjoyed Apophis' pain, Jumar arrived with the news that Netu had become unstable and was going to explode. Apophis took advantage of the moment of surprise to kill the Jaffa and attempted to shoot Sokar with a staff weapon. However, Sokar used his kara kesh's personal shield to block the shot and Apophis ran away, leaving the enraged Sokar behind. Netu exploded shortly afterwards, destroying Sokar's ship and killing Sokar. However, Apophis was able to use the ship's ring transporter to escape to Delmak and took advantage of Sokar's death to take control of Sokar's forces for himself. (SG1: "The Devil You Know")
Aside from the standard Goa'uld traits of arrogance and egotism, Sokar was made infamous for his sadism and cruelty, which were greater than just about any other Goa'uld, aside from Anubis. Sokar would frequently torture people right in front of him and took extra pleasure in prolonging the suffering of his victims to the point of maniacal laughter. This happened to both Jolinar of Malkshur and Apophis during their incarceration on Netu.
Sokar apparently had a fair sense of the Tau'ri version of Hell, and was so inspired by it, he formed his prison world by bombarding the moon from orbit to crack the mantle and allow magma to seep to the surface and turn the sky red. He also was shown to have a militaristic viewpoint on a lot of topics, preferring to dominate via his army. Like other Goa'uld, he had a flair for the dramatic. His speech was twisted, and he usually had a flame nearby.
Sokar has quite a disturbing appearance in his human host. Under Sokar's hood is shown to be a man with pale skin, yellow eyes and prominent black veins all across his face. This disturbing appearance further highlights Sokar's chosen role as the Devil.