Krislok

Krislok was a Graske who encountered Sarah Jane Smith and her friends. He was forced to act as an accomplice of the Trickster.

Biography
The Trickster rescued Krislok from his spacecraft, which had begun to burn up. In return, Krislok became the Trickster's slave. (TV: The Temptation of Sarah Jane Smith) Under orders from by the Trickster, he attempted to erase Maria Jackson from time by kidnapping her and stopping her from ever existing; she had been protected from the Trickster by the Verron soothsayer's puzzlebox. The process went wrong and she briefly ended up in 1964 before being recaptured. Krislok was later sent after her father, Alan Jackson. Alan tied him up and forced him to reveal how to bring Maria "back in time" and rescue her from limbo. Krislok freed himself and teleported away. (TV: Whatever Happened to Sarah Jane?)

Still working for the Trickster, Krislok posed as a human boy named Oscar to lure Sarah Jane to 1951 through a time fissure, to a time just prior to her parents' death, hoping she would save them. The Trickster created an alternate timeline where he manifested corporeally on Earth in 1951. In this timeline, the present day was a desolate wasteland where Krislok enslaved the few surviving humans to mine for resources so he could extend his reach to other planets. Clyde promises Krislok that if he helps them, they will give him the puzzle box to free him from the Trickster. Krislok agrees and re-opened the time fissure to let Rani tell Sarah Jane where the Trickster would manifest. Clyde remained behind, guarded by Krislok. After the timeline was restored and the Trickster defeated, Clyde gave Krislok the box to protect him should the Trickster ever return to punish him. (TV: The Temptation of Sarah Jane Smith)

He did not return with the Trickster when the latter arrived at Sarah Jane's wedding. (TV: The Wedding of Sarah Jane Smith)

Behind the scenes

 * Whatever Happened to Sarah Jane? does not give Krislok's name. This occurred in the second episode of The Temptation of Sarah Jane Smith. Neither episode gives his name in the credits and simply list him as "the Graske".