He came to be known as Kahless the Unforgettable, and he was the Klingon leader who united his people and formed the Klingon Empire in the 9th century in Star Trek. From their home planet of Qo'nos, the Klingon Empire extended their reach throughout the galaxy, and their aggressive colonial philosophy came into conflict with the more benevolent United Federation of Planets when they met in the 22nd century.