Datak Tarr is a fictional male Castithan in the Defiance television series who was portrayed on screen by Tony Curran. Datak is a shrewd businessman whose only in it for himself. When his son Alak Tarr announces that he plans to marry Christie McCawley, Datak sees his opportunity according to Castithan culture on getting his hands on the mine owned by Rafe McCawley. At the end of the first series, he has become mayor of Defiance and seeks a join the Earth Alliance which the previous mayor Amanda Rosewater had fought to oppose.
Although Datak obides by the customs and laws of Defiance, Datak still holds dear to some Castithan traditions. In the opening episode where the city comes under attack, a fellow Castithan does a runner when he gets scared. Datak demands he be punished according to the Castithan traditions.
In the next episode, the coward is captured by Datak Tarr and is tortured in the city square. The ceremony is interrupted by Irisa who frees the coward. Datak takes great exception to this but he backs off when Jeb Nolan appears. Later however when no-one is around, Datak knifes the coward to death.
When Datak is imprisoned at the beginning of the second series, he gets Dr Mew Yewll to perform a sexual act on him which has definitely taken the series in a different direction.