Viktoria (voiced by Terri Brosius) is a woman who contacts Garrett in Thief: The Dark Project, asking him to steal Constantine's sword. However, as later events reveal, she is not a regular human being but is a partner of the Pagan god The Trickster. As such, she becomes one of Garrett's antagonists later in the game.
Viktoria returns in Thief II, but this time allies herself with Garrett as each of them share a common enemy in The Mechanists. As she and Garrett work together against the Mechanists, the two seem to form some sort of a romantic relationship (though this is not ever explicitly made to be the case).
In Thief III she is only referenced to in a letter written by the Pagans that Garrett reads.