Thrax was a Cardassian security officer assigned to Terok Nor in the 2350s. He was replaced by Odo. Odo, Dax, Sisko, and Garak experienced a shared telepathic reality in which Thrax arrested them for the attempted murder of Dukat. They assumed the identities of three Bajorans that were executed for the attempted murder. Even though Thrax could have investigated further and cleared the men, he did not. As the telepathic reality plays out it is discovered that Odo not Thrax was the one who let the prisonners die. (DS9: "Things Past")
- Thrax was played by Kurtwood Smith.