The Jatiri were an ancient and powerful species.
In a timeline in which Emily Rutherford and Tom Charrington separated as teenagers, the Jatiri confronted the Shandance, who had intervened in an interplanetary war. The ensuing 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)