Jacek is a petty thief and con artist and the father of SG-1 member, Vala Mal Doran. He has made a career out of cheating, stealing goods and conducting multi-layered scams.
During his daughter's childhood, he was married to a woman named Adria, whom Vala described as "a witch of a woman." In 2006, Vala named her daughter Adria after her stepmother. (SG1: "Flesh and Blood")
Jacek openly admits he did not raise Vala himself. In fact, he was completely absent for the first three years of her life (a period of time he was black-marketing out of the Nylus sector). According to Vala he would be gone for months at a time, only to return to lay low or to hide from the people he had swindled. Vala looked forward to the few times Jacek was home, and would not let him sleep until he had told her all about his adventures. Though she wouldn't admit it after she had grown to reject him, she kept every treasure of jewelry he brought home for her in a small box, which she keeps to this day. (SG1: "Family Ties")
Following the death of the Jaffa Arkad, Jacek became aware of an Ori plan to attack Earth with Naquadah-heavy Tel'taks. In exchange for the location of the convoy, Major General Henry Landry agreed to allow Jacek to settle on Earth and be near his daughter. Vala was only interested in a relationship with her father if he abandoned his thievish ways, which he attempted to do. But over the course of three weeks he managed to launch a charity phone scam ("little Pepito needs a new pair of kidneys"), marketed glitter shavings called stardust, and draw up plans for a diet book.
Jacek had failed to inform Stargate Command of all of the Naquadah-heavy cargo ships, hoping instead to work with some of Arkad's Jaffa to split the bounty of one of the payloads. SG-1, however, became aware of his plan, and swapped one cargo ship for a decoy without tipping off Jacek or Arkad's Jaffa. To the disappointment of his daughter, who had hoped his desire to embrace new ideals was genuine, Jacek took the bait and departed Earth with the wrong ship.
Only after Jacek had executed the trade on another world did he discover the truth for himself -- that the Naquadah had been switched with lead bars and packing peanuts. Surprisingly, Jacek was able to prevent the deal from going south by convincing the trader that the normal packing peanuts were actually a potent aphrodisiac. (SG1: "Family Ties")
- Jacek is a common given name in Polish (pronouned approximately "YA-tsek"). While it is similar to the Enghlish Jack, "Jacek" originated from the Greek "Hyacinth", whereas "Jack" originated as a diminutive form of "John".