(written from a Production point of view)
Stephen D. Mines (3 February 1939 – 21 May 2019; age 80) was the actor who played Lieutenant Robert Tomlinson in the Star Trek: The Original Series first season episode "Balance of Terror". He filmed his scenes on Monday 25 July 1966 at Desilu Stage 9.
Mines was born in Muskegon, Michigan and was graduated from Muskegon Catholic Central in 1957 and the Pasadena Play house in 1959. He served in the U.S. Army between 1962 and 1964, and moved into acting which he pursued until the early 1970s. He later worked in the furniture business and returned to his birthplace in 2004. He died in Grant, Michigan and is survived by his wife Michele and his son Stephen. 
Mines portrayed characters in 1961 episodes of Bronco, Pete and Gladys and 87th Precinct (starring Robert Lansing), as well as the movie Pirates of Tortuga. He then appeared in the 1962 feature film Mr. Hobbs Takes a Vacation and a 1964 episode of The Lieutenant, created by Gene Roddenberry and starring Gary Lockwood, with the episode also including Joseph Campanella. 1965 saw him in episodes of Paradise Bay, Mr. Novak and Gidget. In 1966, besides Star Trek, he was in episodes of Days of Our Lives and Big Valley.
Mines was a regular cast member on the daytime soap opera As the World Turns from 1966 through 1968. A brief role on Dan August (alongside Ned Romero) in 1971 was his last known television appearance.