Marshal Grover was a wealthy film producer. He was also Amelia Grover's father and Nancy Norton's husband. Professor Sternberg convinced him to finance an expedition to the island of Salutua in 1934. Ostensibly, it was to explore the island and film a King Kong-like movie, with real giant animals instead of special effects. But Grover hoped the cause of the animal's growth could help restore Amelia's missing arm.
Because the Third Doctor created a time bridge to the island from UNIT in the future, several potential timelines were created. (PROSE: The Eye of the Giant)
Original timeline
He died with the expedition when the volcano on the island erupted after Brokk's ship crashed into it.
Alternate timeline 1
Nancy used him to help her take over the Earth.
Alternate timeline 2
He was killed along with everyone else on the planet by the Nancy-Brokk-ship hybrid.
Alternate timeline 3
He saw his daughter transform into a higher being, and her arm restored. He said his goodbyes as she left the planet with the composite creature.