Thetis Island (population: 350) is an island off the coast of British Columbia, Canada. It is one of the Gulf Islands. The island was named in 1851 after HMS Thetis, a 36-gun Royal Navy frigate commanded by Captain Augustus Leopold Kuper (after whom Kuper Island is named). The ship was named after the Nereid Thetis from Greek mythology. Thetis was first settled in 1874 but permanent settlement took hold in the 1890s and 1900s.