Jal Sessen was a male Kazon-Cardassian hybrid and the First Maje of the Kazon-Nistrim sect in the early 25th century. He was the son of Obsidian Order agent Seska and First Maje Jal Culluh and was born in late 2372. (STO - The Delta Quadrant mission: "Alliances", VOY episode: "Maneuvers")
Seska was an undercover agent of the Obsidian Order, disguised as a Bajoran. After she left the Federation starship USS Voyager to join the Kazon-Nistrim, she became pregnant with Maje Culluh's child. During the Voyager-Kazon conflict of 2371-3, Seska informed Commander Chakotay in March 2372 that she had used his DNA to impregnate herself. (VOY episode: "Maneuvers")
When the Kazon captured Voyager and stranded its crew on Hanon IV in late 2372, the Doctor checked the infant Sessen's health and corroborated Culluh's fatherhood. Seska died when the Talaxians aided the Voyager crew in retaking the ship, and Culluh took Sessen with him when the Kazon retreated. (VOY episode: "Basics")
As young boy, Sessen suffered from an infection of mutated dark matter, caused by Ambassador Lhiau when he supplied the Romulan Star Empire with Shepherd technology. Culluh was distraught, and challenged by other Kazon. In 2376, the Entity - a version of Kes from an alternate universe, secretly healed Sessen. Culluh rushed to his son, and his love outcompeted his Kazon anger. (VOY - Dark Matters novel: Ghost Dance)
Sessen grew up disliking the Voyager crew, and probably the Federation by extension. In 2410, Captain Harry Kim held a conference of various first majes in the Bremark system to convince the Kazon sects to join the Delta Alliance and the fight against the Vaadwaur Supremacy. Sessen strong-armed several leaders into supporting him when he turned on the USS Rhode Island and its Kazon allies.
Sessen recognized "Ensign" Kim from his father's stories. His plan had been to take out his grudge on Voyager itself but he found that Kim's Rhode Island sufficed. During the ensuing battle, Maje Sessen was in command of the Nistrim's flagship, the Kazon carrier First Maje of the Kazon-Nistrim. The Kazon-Halik and the Kazon-Mostral sided with the Allies but were defeated. When the Maje was heavily damaged, Sessen warped out of the system but vowed the alliance had not seen the last of him. (STO - The Delta Quadrant mission: "Alliances")
When the Delta Alliance launched its invasion of Vaadwaur Prime later that year, Sessen had covertly convinced the Kazon-Relora to change sides, allying the Nistrim and Relora with Gaul's Vaadwaur. However, Harry Kim and Rear Admiral Tuvok had anticipated that the Kazon might turn on them and called in an allied Hirogen clan to deal with Sessen, who was apparently killed and his ship taken as a battle trophy by the Hirogen chieftain. First Maje Jal Karden of the Kazon-Ogla provided his own sect as reinforcements later in the battle to make up for the Reloras' betrayal. (STO - The Delta Quadrant mission: "Takedown")