A powerful System Lord, Baal is not generally a fair player when dealing with his fellow Goa'uld. He once wiped out 60 million people in two star systems rather than lose them to Sokar during a territorial dispute. If he feels that he has been treated negligently, he has been known to give concealed explosives as gifts.
Baal was one of the System Lords who voted to have Anubis rejoin their ranks, perhaps not totally aware of the implications. Baal was not a System Lord during the era when Anubis was among the highest-ranking Goa'uld, more than a thousand years ago.
He also had a dark and complex relationship with Lord Yu, whom he has been particularly opposed to over the years of the System Lord's reign in the galaxy. But this does not prevent them from meeting for civilized discussion. Yu was the only opposing System Lord (and the only member to survive from Anubis's era), making him a prime target of Anubis.
Anubis sent Baal's forces as a final, crushing blow to Yu and his army -- but Yu managed to escape destruction. He did, however, finally manage to speak reason into Baal, and they unified against Anubis in orbit of Abydos. But Anubis had found the Eye of Ra, the final piece to the puzzle of his super weapon. He destroyed the System Lords' fleet of motherships, presumably including some of Baal's forces.
Following Anubis's defeat, Baal became perhaps the most powerful Goa'uld System Lord -- seizing control of much of his old enemy's territory and resources, including the Kull warriors and some Ancient technology. It was eventually revealed that he was working for Anubis, who had survived the destruction of his fleet.
With Anubis finally defeated once again and the Goa'uld empire brought to an end, Baal had to contend with new challenges -- especially the Ori, against whom he believed himself to be an ally with Earth -- as he fought for power and influence. Baal lived in secret on Earth for a short time, during which he exploited cloning technology to create several copies of himself (both the human host body and the Goa'uld symbiote).
The original Baal was killed when he gated back in time to prevent the existence of Earth's Stargate program, where Cameron Mitchell had previously arrived from the future -- laying in wait and shooting Baal in the head. The man believed to be the final Baal clone was subjected to the Tok'ra's symbiote extraction process; the symbiote died, but the host survived to begin a new life.
Summit - Baal attends the System Lords' summit, and admits that he has suffered heavy losses at the hands of Anubis. He is also an opponent of Yu.
Last Stand - Baal attends the System Lords' summit, voting to allow Anubis back into their ranks.
Abyss - Baal captures Colonel O'Neill, torturing him for information about his lone mission to Baal's secret base. He kills O'Neill over and over, always reviving him with a sarcophagus.
Homecoming - With Lord Yu's health failing, Oshu and Teal'c convince Baal to command the System Lords' fleet against Anubis. He is successful in annihilating the vessel -- though Anubis himself escapes.
Orpheus - The S.G.C. learns that Baal recently took control of Erebus in the name of the United Alliance of the System Lords.
Avenger 2.0 - Baal discovers the Avenger computer virus and modifies the program, transmitting it to all Stargates across the universe, rendering the network inoperative.
Fallout - SG-1 and Jonas learn that Baal ordered Kianna's Goa'uld to Kelowna following Anubis's defeat to learn why Anubis was so interested in the world.
Zero Hour - Baal makes a proposition to General O’Neill: hand over Camulus, and SG-1 will be allowed to return to Earth.
Reckoning, Part 1 - Baal tucks tail and appears on Earth (as a hologram) to request the aid of the S.G.C. in defeating the Replicators, but departs empty-handed.
Reckoning, Part 2 - Baal uses his knowledge of the Dakara super-weapon to help remodulate the device so it will defeat the Replicators, preventing Anubis from taking control.
Threads - Following his betrayal, Baal returns to the feet of Anubis with a well-crafted explanation, but Anubis reveals that he knows of his servant’s betrayal and will only let him live so that he can watch the galaxy crumble.
Ex Deus Machina - Baal provides an ultimatum to the S.G.C.: Allow him to live on Earth in peace or he will detonate a naquadah bomb inside the United States.
Stronghold - A copy of Baal brainwashes half the Jaffa High Council in the hopes that he will eventually control them in the hopes of keeping the Ori at bay.
Insiders - Baal comes to Earth for SG-1's help in capturing his many clones, only to use them in a ruse to capture the S.G.C.'s database.
The Quest, Part 2 - SG-1 finds Baal while searching for Merlin's anti-Ori weapon, and must join forces with him when he claims to have a vital piece of information.
Dominion - Baal takes Adria prisoner as part of a plan to gain control of the Ori forces.
Stargate: Continuum - Baal travels back in time to change Earth's history, making him the most powerful System Lord in the galaxy -- until his queen, Qetesh, turns on him and kills him.