A courier of the 32nd century and wary acquaintance of Cleveland Booker, who sells Book and Michael Burnham out to the Mercantile's enforcers on Hima in 3188 over a stolen cargo.
Cosmo Traitt appears in That Hope Is You, Part 1, the opening episode of the third season. He is one of the couriers who haul goods for the Orion and Andorian bosses running the exchange at Requiem.
Book has taken a cargo that Cosmo regards as his own, and when Book walks into the Mercantile with the newly arrived Burnham, Cosmo is waiting with a weapon. Book in turn has handed Burnham over to the guards, who dose her with a drug that makes her babble the truth.
The stand-off collapses into a running fight across Hima as Book and Burnham flee by portable transporter with Cosmo and the enforcers behind them. The cargo turns out to be Molly, an endangered trance worm.