Final answer:
George Schaller is a biologist who visited Tanzania's Serengeti National Park in the mid-1960s.
Step-by-step explanation:
The biologist who came to Tanzania's Serengeti National Park in the mid-1960s is George Schaller. This rules out Charles Darwin, Jane Goodall, and Dian Fossey for this specific part of history. George Schaller is a renowned field biologist and conservationist who has conducted seminal studies on a variety of wildlife, including the large predators and ungulates of the Serengeti ecosystem.