A nice tribute to him can be found here:
en.chessbase.com/post/estonia-ce … h-birthday
“Grandmaster of Chess: The Complete Games of Paul Keres” is one of the finest chess autobiographies. The games selected are sharp. The annotations are deep and self-critical. I have the little, fat copy of the work which runs to over 570 pages. It is broken up into 3 sections and includes tournament results in each period. I also have a biography written by Fred Reinfeld, “Keres Best Chess Games, 1931-1948” which covers his early period and his first run to try to win the World Champion crown. This book includes more of Keres games and explores his style of play.
Keres started as a correspondence player and a gambiteer. His style evolved into a more positional model when he entered strong round robin tournaments. When you go over a few of his games, you cannot help feeling he was more modern than most of his contemporaries, willing to engage in concrete play rather than rely on systems or technique. He is one of the few great players to feature the Ruy Lopez, with either color, across his career. He made contributions to opening theory in the Ruy Lopez and many other openings. Keres was a great fighter and won games from 9 world champions. It is too bad he never got a chance to play for the title. He was much admired by his colleagues, not only for his chess.
Keres wrote a book with Alexander Kotov, “The Art of the Middle Game.” The section on “How to Defend Difficult Positions,” is chock full of tidbits of advice as well as analysis of specific positions. The section on “The Art of Analysis,” covers how to do deep analysis of adjourned games. While we don’t do adjournments any more, the skills developed by such study can only help a player improve his endgame.