Worf, played by Michael Dorn, is a main character in Star Trek: The Next Generation and in seasons four to seven of Star Trek: Deep Space Nine. He also appears in the films based on The Next Generation. Worf is the first Klingon main character to appear in Star Trek, and has appeared in more Star Trek episodes than any other character. Worf was the only character to be a regular in more than one live-action Star Trek series (While Miles O'Brien was featured in both in The Next Generation and Deep Space 9, he was not a regular cast member in the former series).
Worf was at first not intended to be a regular character, since Roddenberry wanted to avoid "retreads of characters or races featured prominently in the original Star Trek series", and so the June 1, 1987 cast portrait did not include Worf. Several "tall, slim, black actors" auditioned for Worf before Michael Dorn came along, walking into the audition in character and not smiling (Indeed, Michael Dorn found the seriousness of the role, especially during the audition, at first to be uncomfortable, since he considers himself a comedian at heart).
The House of Mogh was a family of high social and political rank which was for a time represented on the Klingon High Council. In Star Trek VI: The Undiscovered Country, Worf's grandfather Colonel Worf (also portrayed by Michael Dorn) appears in a role as the legal advocate of Captain James T. Kirk and Dr. Leonard McCoy after they are accused of killing Chancellor Gorkon of the Klingon High Council. He was also a member of the Klingon delegation at Camp Khitomer. Although not explicitly stated, he was intended to be Worf's grandfather .
Worf was born in 2340 on the Klingon homeworld as the son of Mogh. Five years later, his parents moved to the Khitomer colony. Worf's parents were killed during a surprise attack by the Romulans on the Khitomer outpost. The colony's distress call was answered by the Federation starship USS Intrepid. Chief Petty Officer Sergey Rozhenko found Worf in the rubble and took him in after failing to find any living relatives. Rozhenko and his wife Helena raised him on a small farm colony on the planet Gault, a world of about 20,000 inhabitants, almost all of them human. He also spent time in his parent's native Minsk, later recommending it to O'Brien as one of his favorite places on Earth.
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Official Site: Paramount Television
Links: Worf's Wikipedia Page Worf's Memory Alpha Page TrekCore