Rainer Fritz Albert Knaak (born 16 March 1953 in Pasewalk, Bezirk Neubrandenburg) is a German chess player who holds the FIDE title of Grandmaster (GM).

Prior to unification in 1990, Knaak represented East Germany (otherwise known as the German Democratic Republic) and enjoyed unbridled success in the national championship, taking the title in 1974, 1978, 1982, 1983 and 1984, while finishing a close runner-up in 1975.

Knaak has written a number of books and articles about chess, mostly for ChessBase's publishing wing, where he has been a full-time employee since 1994.

Unlike most grandmaster offerings, his writing is not always confined to the mechanics of the game, but frequently delves into chess history, particularly relating to the famous tournaments and great champions of the past.

His treatise on Paul Morphy, co-written with Karsten Müller, received a complimentary review from critic John Watson, who considered the work would turn out to be more factually accurate than much that had previously been written.