In 2368, he stole a Vulcan transport, the T'Pau, from Surplus Depot Z15 and delivered it to a Barolian freighter at Galorndon Core, near the Romulan Neutral Zone. William T. Riker followed him to Qualor II to seek information about missing Vulcan ships. Omag was thoroughly disreputable and refused to give any information. Riker threatened to revoke his travel in the sector which would severely hamper his arms dealing. After the threat from Riker, he revealed that the Romulans were involved in the theft of Vulcan ships. (TNG: "Unification II")
Background information Edit
The script for "Unification II" describes Omag as, "the fattest Ferengi we've ever seen... on his arms, two gorgeous women in skintight dresses." 
Omag appears in the non-canon video game Star Trek: Elite Force II, voiced by Matt Malloy. In the game, he is a trade working out of a Klingon space station, who is detained by the crew of the USS Enterprise-E for his role in the supply of dangerous weapons of mass destruction. Imprisoned in the brig, Omag eventually reveals whom he sold the weapons to and the location of their control center after the player uses the Ferengi Rules of Acquisition to coerce him without violating Federation regulations on the treatment of prisoners.
Omag is also featured in the Star Trek Customizable Card Game.