Kahless the Unforgettable (Klingon: qeylIS'e' lIjlaHbe'bogh vay') is a fictional character in the Star Trek universe. He is portrayed in Star Trek: The Original Series by Robert Herron and in Star Trek: The Next Generation by Kevin Conway. The character is referenced in media relating to the Star Trek fictional universe, and is a Klingon alien spiritual and historical figure. The character is frequently mentioned in the first season of Star Trek: Discovery. Kahless was also the subject of a Klingon language opera in the Netherlands.