as Gowron, leader of the Klingon Empire. Suzie Plakson as K'Ehleyr, Federation ambassador, mate to Worf and Alexander Rozhenko's mother until her death in 2367. Dwight Schultz as Reginald Barclay, engineering officer until his transfer to Starfleet Communications in 2374. Carel Struycken as Mr. Homn, Lwaxana Troi's attendant. Tony Todd as Kurn, Klingon officer and Worf's brother. Gwynyth Walsh as B'Etor, Klingon officer from the House of Duras and Lursa's sister. Patti Yasutake as Alyssa Ogawa, medical officer and head nurse. Ken Thorley as Mot, barber on the USS Enterprise-D. Daniel Davis as Professor Moriarty as a holodeck character who becomes self-aware. For a more complete list, see Appearances Story arcs and themes Star Trek had a number of story arcs within the larger story, and oftentimes different episodes contributed to two or more different story or character arcs. Some are epitomized by the aliens the characters interact with, for example, TNG introduced the Borg and the Cardassians. The Klingons and Romulans had been introduced in The Original Series (1966–1969); however, the Klingons were somewhat rebooted with a "turtle-head" look, although a retcon was given to explain this in an Enterprise episode. Other story arcs focus on certain peripheral characters such as Q, Ro Laren or characters projected on the Holodeck. Certain episodes go deeper into the Klingon alien saga, which are famous for having an actual Klingon language made for them in the Star Trek universe. The Klingon stories usually involve Worf, but not all Worf-centric shows are focused on Klingons. The Duras sisters, a Klingon duo named Lursa and B'Etor, were introduced on TNG in the 1991 episode "Redemption". They later appeared in the film Generations. One of the science fiction technologies featured in Star Trek: The Next Generation was an artificial reality machine called the "Holodeck", and several award-winning episodes featured plots centering on the peculiarities of this device. Some episodes focused on malfunctions in the holodeck, and in one case how a crew member became addicted to the environment created by the technology. The dangers of technology that allows illusion is one of ongoing themes of Star Trek going back to the 1st pilot, "The Cage" where aliens' power of illusion to create an artificial reality is explored. One of the plots is whether a character will confront a reality or retreat to a world of fantasy. Several episodes in the show also deal with the