Ulis was the captain of a Ferengi ship which raided Enterprise. He and his three-man crew, Grish, Muk and Ulis' inept cousin Krem, managed to gas the Enterprise crew, rendering almost all of them unconscious, and took over the ship. They revived Archer and tried to get him to tell the location of the vault where they assumed the ship's treasure was kept, since they had only found a few largely valueless pieces of equipment. Archer insisted nothing of that sort existed, so the Ferengi decided to take the ship's females to sell at a slave market. To stop them dong so, Archer claimed there was a vault full of hundreds of gold bars but refused to reveal its location unless he was given a share. Ulis decided to search for it himself, taking Grish and Muk with him while Krem stayed to guard Archer and load the stolen equipment on their ship.
Their search naturally yielded nothing, with Ulis' decision to search sickbay and Grish's suggestion it would be in Archer's quarters proving dead end. Muk began to suspect Ulis had misjudged the situation and decided to keep anything he found for himself. T'Pol, who had been revived by Tucker after he escaped the gas by being in decontamination, increased the ill-feeling among the pirates by taking some of Muk's loot and planting it in Ulis' bag.
The Ferengi captured Tucker who pretended to defy Archer's orders and lead the Ferengi to the vault. He proceeded to lead Ulis, Grish and Muk on a lengthy tour of the ship before taking them to a hatch where T'Pol was waiting in ambush and successfully stunned them all. After the Ferengi had been forced to return everything they had stolen, Archer left Ulis, Grish and Muk tied up aboard their own ship which he turned over to Krem, telling them they would stay tied up until they convinced the put-upon Krem to release them.