Agassi got a career grand slam — the only men’s player to do so since Rod Laver. The most Agassi won in one year was three.
Roger Federer has a career Grand Slam, as well, when he won the French Open in 2009, the only Grand Slam event that alluded him up until that time. He also has won 3 out of 4 calendar GS’s three times in his career.
According to the links below Agassi never won three Grand Slam tournaments in the same year. The only Americans to do that were Tony Trabert in 1955 and Jimmie Connors in 1974. In all seven men have won Career Grand Slams: Fred Perry, Don Budge, Rod Laver, Roy Emerson, Andre Agassi, Roger Federer, and Rafael Nadal. Agassi is the only men’s singles player to win a Career Super Slam which consists of the four grand slam tournaments, the Olympics Gold Medal and The ATP World Tour Finals.
https://en.wikipedia.org/wiki/Grand_Slam_(tennis)#Origin_of_the_term_.22Grand_Slam.22
https://en.wikipedia.org/wiki/List_of_Grand_Slam_men%27s_singles_champions