Marc Okrand is the inventor of the Klingon language. He was hired by Paramount Pictures to invent the language and coach the actors on Star Trek III: The Search for Spock, Star Trek V: The Final Frontier and Star Trek VI: The Undiscovered Country.
Marc Okrand is most famous as the author of the dictionary of the Klingon language and all its addenda.
Okrand previously worked with Native American languages, from which he borrowed the unusual Klingon tlh sound (common in North and Central American indigenous languages, in which it is usually transcribed as tl; this is the sound at the end of Nahuatl as the Aztecs pronounced it themselves).
Recent work includes the Atlantean language which he was hired to do for Disney's film Atlantis: The Lost Empire.