According to Dorian Rogozenco Max Euwe’s contribution to the opening theory is unjustly underestimated in the chess world. The former German national trainer points out in his videos that the fifth World Champion introduced the professional approach in studying the openings by analysing theoretical variations and trying to find new ideas and improvements. He contributed in particular to the development of theory in the Slav Defence and Open Variation of the Spanish Game. Rogozenco also concentrates in his videos on two other opening preferences of the fifth World Champion: the Sicilian Defence and the King’s Indian.