Sassacus (Massachuset: Sassakusu (fierce), c. 1560 – June 1637, born near present-day Groton, Connecticut) was a Pequot sachem. He became grand sachem after sachem Tatobem was killed in 1632. Under the sachem Uncas, the Mohegan rebelled against domination by the Pequot. Sassacus and the Pequot were defeated by the English along with their Narragansett and Mohegan allies in the Pequot War.