Robert Stephen Cusack (born 10 December 1950) is an Australian former butterfly and freestyle swimmer of the 1960s and 1970s, who won a bronze medal in the 4x100-metre freestyle relay at the 1968 Summer Olympics in Mexico City.

Cusack combined with Michael Wenden, Bob Windle and Greg Rogers to win bronze in the 4x100-metre freestyle relay, behind the United States and the Soviet Union teams.

He first started competitive swimming at age 9, coached by his father Robert Cusack, and then later during his summer vacations he would travel to Brisbane to train with his uncle Arthur Cusack at the Centenary Pool, Brisbane where his uncle was the lessee of the pool.

Then at night time we'd get into the diving pools and search the bottom for any loose change."

He later went on to become a professional coach commencing at the Indooroopilly Swimming Club in 1977 until his retirement in 2013.