Don Budge is the only man to have won six consecutive major singles titles, from Wimbledon 1937 to U.S. Championships 1938, and the first player ever to complete a Grand Slam (1938). Ken Rosewall holds a record 15 Pro Major titles, and 23 major titles overall, counting both amateur and professional circuits, a record surpassed by Djokovic in 2023.
https://en.wikipedia.org/wiki/List_of_Grand_Slam_men's_singles_champions