On the surface, Muso acted as a liaison between Tellarite military/industrial conglomerate corporations and interplanetary commercial endeavors, and held the position of Administrator. This role placed him quite highly in Tellarite politics. However, he was also had a side-line as a bounty hunter and in various other criminal activities, including murder. Circa 2261, Muso murdered a young Orion woman on Rigel II.
Muso was a delegate at a diplomatic conference held at Babel Station circa 2264, where he continued to conduct his crimes with a group of four humanoid and Tellarite thugs. He gave them a kill-or-capture order on a certain Rigellian for a 10,000-credit bounty, dead or alive. On Babel, he was seduced and nearly assassinated by Leata, the sister of the woman he'd murdered three years before, though the intervention of Fleet Captain Christopher Pike saved him. Muso had smuggled a laser pistol into the conference and tried to kill Leata before she escaped.
Upon further investigation, Pike learned of Muso's highly aggressive personality and criminal activities. Muso ordered that Pike be killed for his suspicions, and his thugs ambushed Pike and Leata as they exited Muso's quarters, having infiltrated them earlier. Muso caught Leata, but she threw him down and nearly killed him in cold blood before Pike persuaded her to spare his life. Soon, the Tellarite criminal was taken into custody by Babel Station security to answer for his crimes. Leata supplied a memory record containing three year's worth of evidence against Muso and a genetic reading to confirm his identity. (ST comic: "Alien Spotlight: Orions")