Sirol did not perform as well as other cadets in Starfleet Academy, but since graduation he has made improvement. He was actually up for promotion to the rank of Commander and was expecting an executive officer position. Sirol was not promoted, however, as his performance was not quite up to par with the other candidates.
Sirol was the head of the USS Mariner's security and served on the bridge at tactical. With a rough personality, Sirol would often prod Captain Gage's darker side to push boundaries more often than he should. He was in space to roam, pillage, and drink. He took the crew's safety very seriously, though.
Sirol maintained friendly banter with Laertezvedha Mundir'Zah, Mariner’s operations manager. The two had a rough beginning when Sirol objected to Dirzah's presence on a dangerous mission. He believed Dirzah was "too green" for such a task, but the Saurian performed well and won his respect. ("A New Threat")
Sirol was the nephew of Torethirala zh'Vres, who was led astray in search of fortune and ended up an accomplice to conspiracy. Sirol never met his aunt, but her reputation was his motivation to not make similar mistakes.
Character biography on Mariner’s official site