'Dexter' Season 7 in 6 Clicks
This season's big bad was Isaak Sirko (Ray Stevenson), a member of the Koshka Brotherhood. He went after Dexter after the blood splatter analyst murdered his lover Viktor (Enver Gjokaj) for killing fellow Miami Metro officer Mike Anderson (Billy Brown). Though he caused much havoc during the season, Isaak eventually asked Dex for help (he said in other circumstances the two could have been great buddies) in taking out the hitman his former henchman George took out on him. He died on Episode 9.
Source: Robert Tepper/Showtime