Simpkins studied at the Winnipeg School of Art and his first job was as a commercial illustrator for the Hudson's Bay Company's Beaver Magazine. During World War II Simpkins joined the army medical corps as an illustrator and in 1945 went to work in Ottawa as a film strip artist for the National Film Board. His endearing Jasper character was originally conceived as a polar bear for a proposed comic strip. Maclean's editor Jerry Anglin, however, suggested the character's wry sense of humour was more suited to that of a friendly black bear.

Jasper first appeared in the magazine on 1 December 1948, was on the cover 5 times, and in 1967 was syndicated as a cartoon strip. The cartoon character was also the subject of 5 books. Jasper became so popular in English Canada that Peter C. Newman, observing that Jasper captured our national character so well, suggested that "someday we may even change our national emblem from a beaver to a bear." Jasper ran until 1972 when Simpkins retired. In addition to Jasper, Simpkins did monthly cartoons for The Medical Post which were collected and published as When's The Last Time You Cleaned Your Navel? In 1994, he received the first Lifetime Achievement Award presented by the Toronto Cartoonists Society.