Then, with David de Keyser, he started The London Studio, which taught method acting to British actors.

He is best known for his roles in Spaghetti Western films, most notably in his two collaborations with Sergio Leone, The Good, the Bad and the Ugly and Once Upon a Time in the West.

Mulock died by suicide by jumping from his hotel room in Guadix, Granada, Spain, in May 1968, while filming for Once Upon a Time in the West.

[3] Mickey Knox, screenwriter for the film, and production manager Claudio Mancini witnessed Mulock's suicide as his body passed their hotel window near the end of the shoot.

Mulock survived the fall, but suffered a pierced lung from a broken rib during the bumpy ride to the hospital.