Roy Cohn's famous 52nd birthday party was held at
Studio 54 on
February 22, 1979. (Though he turned 51 when he first started celebrating there in 1978, his most infamous, widely documented bash happened in early 1979).
The person famously dressed in the Roman outfit—specifically a
winged Roman god costume representing Mercury/Hermes—was the performance artist, designer, and Andy Warhol superstar
Victor Hugo.
Hugo, who was also the partner of fashion designer Halston, was known for pulling avant-garde stunts at Studio 54 and frequently appeared in Roman garb or togas.