A renegade Vulcan agent whom a young T'Pol shot dead on Risa while hunting fugitives for the Ministry of Security, a killing so distressing that the memory was ritually suppressed.
Jossen is seen only in T'Pol's recovered memories in the second-season Enterprise episode The Seventh. He was one of several Vulcan undercover operatives on Agaron who refused to come home when their assignment ended.
T'Pol, then new to the Ministry of Security, was sent to bring the agents back. She chased Jossen and his companion Menos to Risa, where she cornered Jossen and fired when he seemed to reach for a weapon. Unable to live with the doubt and guilt that followed, she underwent the fullara ritual at P'Jem, which buried the memory.
When she is ordered to capture Menos in 2152, the memory of Jossen returns and nearly wrecks the mission, until Archer helps her to face what happened.