John Murice Jackson (born June 1, 1950) is an American actor, best known for playing Rear Admiral A. J. Chegwidden on the CBS series JAG and also as a special guest star on its spin-off NCIS and recurring cast to its spin-off NCIS: Los Angeles.John was forced to use his middle initial "M." for his professional name because there was already a "John Jackson" registered with the Screen Actors Guild when he joined the union and SAG rules prohibit two or more members from using exactly the same name.