Read more about Night King at: Wikipedia

Official Site: George R. R. Martin

The Night King is a fictional character appearing in the HBO high fantasy television series Game of Thrones, based on George R. R. Martin's novel series A Song of Ice and Fire. He is depicted as the leader and the first of the White Walker, having existed since the age of the First Men, and is the most dangerous and powerful of his race. The Night King is an original creation of the television adaptation, thus far having no counterpart in the novels upon which the show is based.

The Night King was portrayed by British-American actor Richard Brake in seasons 4 and 5 and then by Slovakian actor and stuntman in seasons 6 to 8.

In Game of Thrones, the Night King is physically distinguished from the other White Walkers by his "crown" of pointy, frosty horns.

The "Night King", as presented in the show, has not appeared in A Song of Ice and Fire. In the novels, the title "Night's King" is given to the long-ago legendary 13th Lord Commander of the Night's Watch, who supposedly married a female White Walker and led the Night's Watch to commit atrocities.

Night King has not been a contender in any CBUB matches.