(written from a Production point of view)
Roger C. Carmel (27 September 1932 – 11 November 1986; age 54) was a rotund character actor and sometime comedian whose trademark was a handlebar mustache. He is most famous for playing the role of Harcourt Fenton "Harry" Mudd on Star Trek: The Original Series in the episodes "Mudd's Women" and "I, Mudd". With the exception of those actors who played USS Enterprise crew members on the series, Carmel is the only actor to play the same character in more than one episode of TOS. He also voiced the character in an episode of Star Trek: The Animated Series, "Mudd's Passion".
Early career (1958-1960s)
Born in Brooklyn, New York, Carmel broke into film in 1958. That year, he made an uncredited appearance in the film Stage Struck. Starring in that film were fellow Star Trek alumni Christopher Plummer and John Fiedler. Carmel went on to have larger roles in the films A House Is Not a Home (1964, with Stanley Adams), The Silencers (1966, with James Gregory, Grant Woods, and Nancy Kovack), and Gambit (1966, with John Abbott and Vic Tayback).
He began working in television in the early 1960s, appearing on programs such as Naked City, Car 54, Where Are You?, The Dick Van Dyke Show, The Munsters, The Man from U.N.C.L.E., and I Spy. In addition to playing Harry Mudd, he is also well-remembered by fans of the 1960s Batman television series as Colonel Gumm, a stamp obsessed, identity swapping villain who very nearly gummed, perforated, and coiled Batman and Robin.
Carmel was a regular on the NBC sitcom The Mothers-In-Law during the 1967-68 TV season, where he played the role of Roger Buell. After the show's first season, NBC opted to renew the series for a second season, but due to less-than-spectacular ratings, the network was unwilling to pay any increases in budget or salary. The entire cast and crew of the show agreed to forgo salary increases to keep the show on the air, with the exception of Carmel, who threatened to quit unless he was given a second season raise. The producers were left with no choice but to fire Carmel and replace him. Afterward, Carmel found it difficult to procure a regular role on an ongoing television series. 
Later career (1970s-1986)
In 1971, Carmel appeared in an episode of Ironside with TOS castmate William Shatner. Carmel's television work during the 1970s also included appearances on The High Chaparral (with Henry Darrow and Malachi Throne), Hawaii Five-O (including a two-parter with Sabrina Scharf and directed by Michael O'Herlihy), Banacek (in an episode written by Stephen Kandel that co-starred Logan Ramsey and David Spielberg and was directed by Lou Antonio), Chico and the Man, All in the Family, and Three's Company. His film credits during this period included the 1970 adventure film Skullduggery (with William Marshall and Booker Bradshaw), Clint Eastwood's 1973 romantic drama Breezy, and the 1977 adventure film Thunder and Lightning. The latter picture was directed by Corey Allen and also starred George Murdock and Charles Napier.
In 1980, Carmel co-starred with Susan Oliver in the Jerry Lewis comedy film Hardly Working. The following year, Carmel won the regular role of Lawrence Brody in the NBC series Fitz and Bones, on which he co-starred with TNG actress (and fellow two-time TOS guest star) Diana Muldaur. The series only lasted five episodes, but Carmel and Muldaur would reprise their characters in a 1982 Fitz and Bones TV special entitled Terror at Alcatraz.
After the failure of Fitz and Bones, Carmel performed primarily as a voice actor, most notably for the animated series Transformers, on which Michael Bell also worked. He and Bell went on to voice for the feature-length The Transformers: The Movie, along with TOS star Leonard Nimoy. His voice work also included My Little Pony and Friends and Disney's Adventures of the Gummi Bears and DuckTales.
Carmel was also the voice of Smokey the Bear in countless Forest Service public service commercials throughout the 70s and 80s. In addition, he found success in commercials for the Mexican fast food restaurant chain, Naugles, for which he played Señor Naugles, a kindly, old Mexican general.
Carmel continued to work steadily doing both voice-over work and the Naugles commercials until 1986, when, on 11 November, he died of a massive heart attack due to complications from atherosclerosis and an enlarged heart muscle, a legacy of chronic alcoholism and drug abuse. He was 54 years old.
There have been varying reports as to Carmel's cause of death. The statement originally released to the public at the time of his death stated that he had committed suicide by overdosing on aspirin. Another story has been relayed by a male prostitute who claimed to have frequented Carmel's home. According to this story, Carmel died of an accidental crack cocaine overdose while celebrating his new-found good fortune.  These claims, however, were not confirmed. The official cause of death is hypertensive cardiomyopathy (heart disease).