Rainer was born in Baden, Austria. During his early years, he was influenced by Surrealism. In 1950, he founded the Hundsgruppe (“dog group”) together with Ernst Fuchs, Arik Brauer, and Josef Mikl. After 1954, Rainer’s style evolved towards Destruction of Forms, with blackenings, overpaintings, and maskings of illustrations and photographs dominating his later work.