(written from a Production point of view)
Marianna Hill (born 9 February 1941; age 79) is an actress who portrayed Doctor Helen Noel in the Star Trek: The Original Series first season episode "Dagger of the Mind" in 1966. She filmed her scenes between Thursday 11 August 1966 and Wednesday 17 August 1966 at Desilu Stage 9 and Stage 10.
Hill was born in Santa Barbara, California, lived in several countries as a child and learned a number of accents. This, combined with a vaguely foreign beauty, earned her a number of feature film and television roles. She worked steadily from the early 1960s until the early 1980s. Her film work included a number of B-movies, such as The Invisible Strangler. She is cousin to retired American general Norman Schwarzkopf and artist/entrepreneur Stephen Hutchison. Hill and John Anderson appeared in the Perry Mason episode "The Case of the Greek Goddess".
Hill left Los Angeles in the 1980s and moved to New York to teach at the Lee Strasberg Theatre and Film Institute. Her final film in America was Chief Zabu, filmed in 1986 but not released until 2016. She then moved to England in 1988 to teach at The Lee Strasberg Studio in London. She remained there until its closure in 2001. Hill continued to teach at The Method Studio in London, and made an appearance in the 2005 British film Coma Girl: The State of Grace, a part she got through the association of one of her students with the film's writer and director Dina Jacobsen. 
There is an English actress named Maryann Hill who joined the Screen Actors Guild in 1941. The two are constantly confused and Marianna Hill has been given many of Maryann Hill's credits.
- Gunsmoke episode "Pa Hack's Brood" (1963, with musician Carl Fortina)
- The Outer Limits episode "I, Robot" (1964, with Leonard Nimoy, John Hoyt and Peter Brocco)
- Paradise, Hawaiian Style (1966, with Julie Parrish)
- The Wild Wild West episode "The Night of the Bogus Bandits" (1967, with Michael Dunn)
- The Traveling Executioner (1970, with Graham Jarvis, James Sloyan, Stefan Gierasch, Logan Ramsey and James Greene)
- Blood Beach (1981, with Stefan Gierasch, Ian Abercrombie and Bobby Bass)