Theodore Tillman Shackelford III (born June 23, 1946) is an American actor, known for his roles on television. He played Gary Ewing in the CBS prime time soap operas Dallas and its spin-off Knots Landing (1979–1993),^[3] and had a recurring role portraying twin brothers William and Jeffrey Bardwell on the CBS daytime soap opera, The Young and the Restless (2006—2015).

Shackelford was born in Oklahoma City, Oklahoma, and went to college at the University of Denver. He appeared in the role as Ray Gordon on the daytime soap opera Another World from 1975 to 1977. He later appeared on prime time series Wonder Woman and The Rockford Files, before was cast as Gary Ewing, the middle son of oil baron Jock and Miss Ellie Ewing, the father of Lucy Ewing and the husband of Valene Ewing in the CBS prime time soap opera, Dallas in 1979. The role was originally played by actor David Ackroyd, who was unable to return for future appearances after his 1978 turn as the character. Shackelford later became one of the main stars of the CBS television series Knots Landing, in which he starred from 1979 to 1993.^[4] He later starred in the 1997 miniseries, Knots Landing: Back to the Cul-de-Sac.

Shackelford starred in the 1987 adventure film Sweet Revenge opposite Nancy Allen making his big screen debut.^[5] He guest-starred on Soap, Hotel, Alfred Hitchcock Presents, The Twilight Zone and The Young Riders during his Knots Landing years. He starred in the made-for-television movies Baby of the Bride (1991), Mother of the Bride (1993), Dying to Remember (1993), Sweet Temptation (1996) and Stolen Women: Captured Hearts (1997). From 1994 to 1995, Shackelford starred in the British science-fiction series, Space Precinct. He had a recurring role in the 1996 The WB prime time soap opera, Savannah, and the following years appeared on Cybill, The Outer Limits, The Practice and Dirty Sexy Money.

On February 2, 2006, Shackelford joined the cast of the daytime soap opera The Young and the Restless as Genoa City district attorney William Bardwell.^[1] His last air date on the popular soap as William Bardwell was on July 18, 2007, when his character succumbed to complications caused by a stroke.^[6] However, on August 7, 2007, Shackelford returned to the show as Bardwell's identical twin brother, Jeffrey Bardwell. He last appeared in series on January 9, 2015.

In 2013, Shackelford reprised the role of Gary Ewing in three episodes during the second season of Dallas series on TNT, in one of which he was reunited with Joan Van Ark as Valene.^[7][8]