Joseph Weider (; November 29, 1919 – March 23, 2013) was a Canadian bodybuilder and entrepreneur who co-founded the International Federation of BodyBuilders (IFBB) alongside his brother Ben Weider. He was also the creator of the Mr. Olympia, the Ms. Olympia and the Masters Olympia bodybuilding contests. He was the publisher of several bodybuilding and fitness-related magazines, most notably Muscle & Fitness, Flex, Men's Fitness and Shape, and the manufacturer of a line of fitness equipment and fitness supplements.