Laurie Strode
Judith Margaret Myers (Sandy Johnson), also known simply as Judy (November 10, 1947 - October 31, 1963; according to the headstone in John Carpenter's film), is the older sister of Michael Myers, as well as the biological sister of Laurie Strode. She was a victim of sororicide at the age of fifteen (10 days shy of sixteen). In "Halloween H20", Keri Tate/Laurie Strode reveals to her boyfriend that her sister Judith was seventeen years old when she died. This was incorrect and most likely written in the script so that it would correlate with Laurie's age when Michael tried to murder her in 1978 and Laurie's son John's age in the present setting of 1998. Her murderer was her brother Michael, aged six.