Tregaar was a resident of Tellar at the time of the creation of the Demilitarized Zone, and followed the deteriorating situation there via news reports. He grew disillusioned with the Federation for having abandoned its people, and left Tellar to join the Maquis.
In early 2373, Tregaar was part of a Maquis cell led by Maass. Their cell was to meet with another cell in the Salva system to hand off a Klingon sensor shield. However, both Maquis ships were attacked by Cardassian forces and heavily damaged before Commander William T. Riker, aboard the shuttle Anaximenes, was able to blind the Cardassians' sensors and allow them to land on a moon of Salva IV. Maass agreed to turn over their Klingon technology in return for help from Starfleet; Tregaar, though, convinced him to instead turn over a collection of antiquated Klingon weapons. Tregaar also violently confronted Riker and Lieutenant Padraig Daniels in order to escape their custody aboard the Maquis ship Liberté. (TNG - Slings and Arrows eBook: A Weary Life)