Which character in Lost was a former Iraqi Republican Guard torturer?

Sayid Jarrah was a former Iraqi Republican Guard torturer in Lost.

Sayid is introduced as an experienced communications officer and soldier among the survivors of Oceanic Flight 815. His technical knowledge and military training make him valuable when the group needs equipment repaired, signals interpreted, or threats assessed.

The series explores his struggle with violence and remorse through flashbacks. Sayid’s past as an interrogator contrasts with his repeated efforts to protect other survivors and use his skills for their benefit.

This answer concerns Sayid’s occupation and history, not his nationality. Sayid is Iraqi, but the question asks for the character who held the specific role of Republican Guard torturer before the crash.