Any person that has won a Triple Crown Championship or a Grand Slam Championship. Any Grand Slam Champion is also a Triple Crown Champion by extension, includes both formats.
Women's Triple Crown= RAW Women's Title, Smackdown Women's Title and WWE Women's Tag Team Title.
Women's Grand Slam= Women's Triple Crown + NXT Women's Title.
Tag Team Triple Crown= RAW Tag Team Title, Smackdown Tag Team Title and NXT Tag Team Title.
NXT Triple Crown= NXT Title, NXT Tag Team Title, and NXT North American Title
Modern Grand Slam= At least one WWE/Universal Title, WWE/RAW/Smackdown Tag Team Title, Intercontinental and U.S Title
Triple Crown= at least one World Title, Intercontinental and Tag Team Title
Classic Grand Slam= at least one WWE/F Title, World Heavyweight Title, WWF/World Tag Team, WWE Tag team, Intercontinental and Hardcore/European Title
WWE have said that the Universal title is eligible for Grand Slam status, but they've not said it's eligible for Triple Crown status. As such, he's not technically a Triple Crown champion. Should that change, he'll be added.