Krislok

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

The Trickster rescued Krislok from his spacecraft, which had begun to burn up. In return, Krislok became the Trickster's slave. 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 puzzle box. 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.

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. Krislok 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.

He did not return with the Trickster when the latter arrived at Sarah Jane's wedding.

_{Biography from the TARDIS Data Core article, licensed under CC-BY-SA}