Ulic Qel-Droma is a human Jedi from Alderaan, born to the Jedi Master Lien-Tsai Qel-Droma and trained alongside his brother Cay and the Twi'lek Tott Doneeta under Master Arca Jeth on Arkania. He is the protagonist of Tom Veitch's Tales of the Jedi, first published by Dark Horse Comics on 1 October 1993 — though he was mentioned earlier still, in Veitch's endnotes to Dark Empire.
Onderon first
His first mission, in 4000 BBY, is to end the centuries-long Beast Wars on Onderon. He and his companions arrive on the side of the walled city of Iziz, work out that the monarchy is the problem, and switch. It is a good opening: the Jedi as arbitrators who can be persuaded they have backed the wrong party.
The plan
After the dark side kills Arca Jeth at Deneba, Qel-Droma announces that he will infiltrate the Krath — a dark-side society running the Empress Teta system — and destroy it from within. Every other Jedi in the story tells him this will not work. Nomi Sunrider tells him twice. He goes anyway, and by the time he has finished he is a warlord commanding the Krath military and the apprentice of Exar Kun.
The Great Sith War
Qel-Droma brings the Mandalorian Crusaders under Mandalore the Indomitable into the war by beating him in single combat, raids the library world Ossus, and kills his own brother Cay on the field — the moment the whole serial has been building to, and the moment it breaks him.
The wall of light
What follows is the most striking thing in Tales of the Jedi, and one of the strangest punishments in Star Wars. Nomi Sunrider does not kill him. She severs him from the Force entirely: a wall of light, a fortress, and a man left alive inside it with nothing. He spends the rest of his life as an ordinary person who used to be able to do everything.
Redemption
The final arc, Redemption (1998), is set ten years later on the ice world Rhen Var, and gives him a last act as a teacher: he trains Vima Sunrider, Nomi's daughter, in a discipline he can no longer practise. He is killed there in 3986 BBY by a blaster shot from a bystander, which is the correct ending for him and reads as an anticlimax on purpose.
Why he lasts
Because he is the Expanded Universe's first serious attempt at a fall that is neither seduction nor accident. Qel-Droma is not tricked. He is competent, well-intentioned, and certain that the rules about the dark side do not apply to a sufficiently disciplined person — and the story spends five arcs demonstrating, patiently, that they do.