William Casper was born in Wisconsin and grew up in a rural area near Lake Winnebago. He developed an interest in fishing at a young age, encouraged by his uncles. Casper's career began at Giddings & Lewis, a machine shop in Fond du Lac, where he worked as a machinist and eventually became a maintenance foreman. His passion for fishing, particularly sturgeon spearing, led him to become an advocate for the conservation of the species.