John Murice Jackson (born June 1, 1950) is an American actor, who played Rear Admiral A. J. Chegwidden on the CBS series JAG and was also a special guest star on the spin-off NCIS, and recurring cast to its spin-off NCIS: Los Angeles. Jackson uses 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. (Via Wikipedia)