Trivia

Has played a JAG (Judge Advocate General) officer in two different works, A Few Good Men (1992) and JAG (1995), and a retired JAG officer in two additional works, NCIS (2003) and NCIS: Los Angeles (2009), with "JAG," "NCIS," and "NCIS: Los Angeles" being the same character, Albert Jethro Chegwidden (better known as Rear Admiral A.J. Cegwidden, USN (Ret.)).

He was a social studies teacher (1975-1979) at Lyndon Baines Johnson High School in Austin, Texas.

Son Conor Jackson was briefly (most of 2006) the everyday First Baseman for the Arizona Diamondbacks, before splitting his time at the end of 2006 through his June 15. 2010 trade to the Oakland Athletics playing First Base and Left Field.

While preparing for the role of A.J. Chegwidden in JAG (1995), he interviewed several senior naval officers to get a better idea of how to play an admiral. Reportedly, the common response was "An admiral acts any damn way he wants to!".

When he joined SAG (Screen Actors Guild), he was forced to use his middle initial, M, professionally, because there was already a "John Jackson" registered with SAG, and union rules prohibit two or more members from using exactly the same name.

He attended and graduated from the University of Texas at Austin.

He was born in Baton Rouge, Louisiana, but was raised in Fort Worth, Texas, where he attended Arlington Heights High School, playing football and basketball there, graduating high school class of 1968.

Began acting at community theater while in his late 20s. before moving to New York City in 1980 to pursue an acting career.

Son, Conor, was traded by the Arizona Diamondbacks (for Sam Demel, plus cash) to the Oakland Athletics on June 15, 2010, and traded by the Athletics to the Boston Red Sox on August 31, 2011 (for a minor league player), with his last regular season, Major League game, being played in a Boston Red Sox uniform, on September 19, 2011, finishing his Major League career with a grand slam home run.

His son Conor was born on 7 May 1982 in Austin, Texas

Has one daughter, Katherine.

His son, Conor Jackson, was a First Baseman in the Arizona Diamondbacks minor league organization, before making his Diamondacks Major League debut on July 28, 2005, against the Chicago Cubs at Wrigley Field. His time with the Diamondbacks organization came to an end when he was traded to the Oakland Athletics on June 15, 2010.

When John M. Jackson was on JAG as AJ Chegwiddon, the initials AJ stood for Albert Jethro. When He was introduced on NCIS:Los Angeles, the initial A in AJ stood for a different name even though he played the same character.