Shandance

The  were an ancient and powerful species.

In a timeline in which Emily Rutherford and Tom Charrington separated as teenagers, the Shandance were forced to intervene in an interplanetary war. They were confronted by another ancient species, the Jatiri, and the resulting battle, called the Collision, resulted in the end of the universe. When the Third Doctor encouraged Emily and Tom to stay together, the timeline was averted, and interplanetary war was avoided. (PROSE: Separation Day)