Sternberg was an eccentric professor, and a former medical doctor in Switzerland, before an operation resulted in the death of a young girl; although he was cleared of malpractice, the girl's family were influential enough to get him charged with misjudgement.
Exiled from Europe, he researched the legends surrounding Salutua, and discovered its location after treating a man found in the Pacific with giant animal bites. He convinced Marshal Grover to finance an expedition to the island. 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 his daughter 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. However, in all of them, Sternberg was killed. In the original, he died with the expedition when the volcano on the island erupted after Brokk's ship crashed into it. In the others, Nancy Grover killed him to get the Semquess drugs he had stolen. (PROSE: The Eye of the Giant)