Jonah Summerfield III was the grandfather of Bernice Summerfield. He shared his name with his two earliest known ancestors: Jonah Summerfield I and Jonah Summerfield II.

He was conceived in the mid-25th century by Dylan Summerfield II and a woman who - according to late 26th century records - may not have been human. In 2455, it was discovered that Dylan was sleeping with non-humans and Jonah was separated from his father.

When he grew up, Jonah joined Spacefleet. He became an officer and gained numerous medals during his service.

Sometime during his life, Jonah had a son whom he named Isaac Summerfield after his great-grandfather. (PROSE: Dead Romance)