Question: what english actor was best known for his role as Giles French and a detective series Checkmate?

Context paragraphs:
Checkmate (TV series): Checkmate is an American detective television series starring Anthony George, Sebastian Cabot, and Doug McClure.  The show aired on CBS Television from 1960 to 1962 for a total of 70 episodes and was produced by Jack Benny's production company, "JaMco Productions" in co-operation with Revue Studios.  Guest stars included Charles Laughton, Peter Lorre, Lee Marvin, Mickey Rooney and many other prominent performers.

Raymond Francis: Raymond Francis (6 October 1911 – 24 October 1987) was an English actor best known for his role as Detective Chief Superintendent Tom Lockhart in the Associated-Rediffusion detective series "Murder Bag", "Crime Sheet" and "No Hiding Place".  He played the role of Lockhart in these series from 1956 to 1967, and the character was one of the first recurring television detectives.

Trevor Eve: Trevor John Eve (born 1 July 1951) is an English film and television actor.  In 1979 he gained fame as the eponymous lead in the detective series "Shoestring" and is also known for his role as Detective Superintendent Peter Boyd in BBC television drama "Waking the Dead".  He is the father of three children, including actress Alice Eve.

David Leon: David Jeremy Leon (born 24 July 1980) is an English actor, director, writer and producer.  As an actor, he is best known for appearing in photographer Rankin's directoral debut "Lives of the Saints" as Othello and Guy Ritchie's film "RocknRolla".  From 2011 to 2014, he co-starred with Brenda Blethyn in the ITV detective series "Vera."  Leon has directed several short films "Father", "Man and Boy" and "Orthodox".  He completed his first feature-length film, also called "Orthodox", in 2015.

Ken Lynch: Kenneth E. "Ken" Lynch (July 15, 1910 – February 13, 1990) was an American radio, film, and television actor with more than 180 credits to his name.  He was generally known for portraying law enforcement officers and detectives.  He may have been best known for his starring role as 'the Lieutenant' on Dumont detective series "The Plainclothesman" (1949–54), on which his face was never seen, and for his co-starring role as Sergeant Grover on "McCloud".

Brenda Blethyn: Brenda Anne Blethyn, OBE (née Bottle; 20 February 1946) is an English actress who has worked in theatre, television and film, best known for her role in Mike Leigh's 1996 drama "Secrets & Lies", and, from 2011, for the title role in the TV detective series "Vera".

Jane Wymark: Jane Wymark (born 31 October 1952) is an English actress.  The daughter of English actor Patrick Wymark (1926–1970) and the American writer and playwright Olwen Wymark, she is best known for playing Morwenna Chynoweth Whitworth (Morwenna Carne by the close of the series) in the 1970s BBC television period drama "Poldark" (1977), and more recently as Joyce Barnaby (1997–2011) in the ITV detective series "Midsomer Murders".  She has appeared in UK television dramas such as "The Bass Player and the Blonde", "A Touch of Frost", "Dangerfield", "Lovejoy" and "Pie in the Sky".  She also appeared as Jill Mason in the Birmingham Rep production of "Equus".

Tina Cole: Tina Cole (born August 4, 1943) is an American actress and singer.  She is best known for her role as Katie Miller Douglas on the 1960s sitcom "My Three Sons" (1967–72), but she previously had a recurring role as Sunny Day in the detective series "Hawaiian Eye" (1963).  She was also a member of the Four King Cousins, a subgroup of the King Family Singers.  In 1963 she played the minor (uncredited) role of Ruth Stewart in "Palm Springs Weekend", a spring break party film set in Palm Springs, California.

Van Williams: Van Zandt Jarvis Williams (February 27, 1934 – November 28, 2016) was an actor best known for his leading role as Kenny Madison in both Warner Bros. television detective series "Bourbon Street Beat" (1959-60) and its sequel, "Surfside 6" (1960-62).  He teamed for one season with the late Bruce Lee as his partner Kato, in the television series "The Green Hornet", broadcast on ABC during the 1966–67 season.

Sebastian Cabot (actor): Charles Sebastian Thomas Cabot (6 July 1918 – 22 August 1977) was an English film and television actor, best remembered as the gentleman's gentleman, Giles French, opposite Brian Keith's character, William "Uncle Bill" Davis, in the CBS-TV sitcom "Family Affair" (1966–1971).  He was also known for playing the Wazir in the film "Kismet" (1955) and Dr. Carl Hyatt in the CBS-TV series "Checkmate" (1960–1962).

Supporting paragraphs: Checkmate (TV series) Sebastian Cabot (actor)
Answer: Sebastian Cabot