Harlequin is a star system with two Class M worlds: Harlequin-3 (also known as Vardaine) and Harlequin-5 (also known as Aloysia). While Vardaine is an Earth colony affiliated with the United Federation of Planets, Aloysia is a non-Federation world heavily influence by the Elasi pirates.

In 2268, the USS Enterprise was sent by the Starfleet to investigate the number of Elasi ships. Harry Mudd's salvage activities near Aloysia and the neighboring Elasi-controlled Harrapa system had provoked the Elasi into attacking his Federation]]-registered vessel. When the Enterprise fought off the two Elasi ships and Mudd's ship left for Harrapa. (TOS video game: 25th Anniversary)