As the son of Gregory Kelswa-Steiner, governor of Prefecture IX of the Republic of the Sphere, he was part of the ruling family of Skye and Heir-Apparent to the throne. Inheriting the title of Landgrave, he was always at odds with his father, growing up believing that the Republic was a poor steward to the Skye people's ambitions for freedom.
After hearing word of militia factions raising armies to claim parts of the Republic, he formed the Stormhammers. Declaring support for House Steiner, his charisma allowed him to take most of Prefecture IX's standing military forces with him.
In August 3133 the Jasek led the Stormhammers on a raid on Towne; Jasek had assistance from Lohengrin in modifying a number of Garrot Superheavy Transports that the Stormhammers had seized from the Skye militia which played a key part in the raid. The modifications made the Garrots resemble Skystar Freight Helicopters, ubiquitous civilian cargo haulers. The Stormhammers used these modified helicopters to infiltrate commandos into the Prince John spaceport, seizing the facility easily. The destruction of a sizeable number of Skystars in future years may well be a result of the Jasek's raid on Towne.
In 3134, Prefecture IX was invaded by a Clan Jade Falcon military expedition. After claiming a number of worlds in the old Isle of Skye region of the Republic, Jasek activated his forces after Tara Campbell's Northwind Highlanders and Skye's remaining militia forces managed to defeat the Falcons on Skye. He then mustered his forces and rescued elements of the Northwind Highlanders who were stranded in Falcon-controlled space. He then presented himself and his forces to Campbell and his father in a bid to fight off the Falcon's invasion. He began a relationship with Campbell, though did not reveal his feeling for her.
Jasek advocated that the forces stationed in Skye were insufficient to withstand another invasion. He then proposed to gather reinforcements, while Prefecture IX's defenders conducted strikes against Falcon held worlds.
After meeting with Anastasia Kerensky's Steel Wolves, he convinced the renegade faction to join the fight for Skye. He then retook a Lyran world that was captured by Falcons during the beginning of their invasion. Heading to the Lyran Commonwealth and convincing Hesperus II's Duke Vedet Brewster to lend him forces and the WarShip LAS Yggdrasil for the battle for Skye, he also revealed his plans to bring Skye back to Lyran control to the Duke and Archon representative Trillian Steiner.
By early 3135, Jasek's Forces arrived in the Skye system, escorted by the Yggdrasil, to confront the second invasion of the Jade Falcons. In a number of clashes battling for the planet, Skye forces were nearly ruined attempting to fight off the invasion led by Malvina Hazen. He saved his forces and his allies, using Clan hegira. This allowed his and other forces to withdraw from Skye under ceasefire. Jasek led these forces to the Stormhammer-held world of Nusakan. There he and his father had one last meeting, where his father accused his son of deliberately allowing Skye to fall so he could reclaim the world himself.
Jasek was later seen on Terra at the funeral of Victor Steiner-Davion as part of the Lyran Commonwealth's funeral delegation. He met Tara Campbell again and tried to resume his courtship with her. He participated in the re-enactment of the War of 3039, where he led the Steiner forces in an invasion of the Draconis Combine. During the Simulation he was defeated by Alaric Wolf, who volunteered to fight on the Steiner front of the war.
During the Skye campaign, Jasek piloted a Templar OmniMech which appeared to have a fixed weapons configuration.
It is unclear what happened to Jasek Kelswa-Steiner after events of Victor Steiner-Davion's funeral. Stormhammer forces are seen fighting Clan Wolf invasion of former Prefecture IX in 3137 without Jasek leading them.
- Technical Readout: 3145 Mercenaries, p. 12, "Garrot Superheavy Transport"