Ivan Lendl (born March 7, 1960) is a former World No. 1 professional tennis player. Originally from Czechoslovakia, Lendl later became a United States citizen. He was one of the game's most dominant players in the 1980s and remained a top competitor into the early 1990s. Tennis magazine named him as one of the ten greatest tennis players since 1966, calling him "the game's greatest overachiever" and emphasizing his importance in the game's history. In his book Modern Encyclopedia of Tennis, Bud Collins included Lendl in his list of the 21 greatest male tennis players for the period from 1946 through 1992.

Lendl captured eight Grand Slam singles titles. He competed in 19 Grand Slam singles finals, a record for a male player since surpassed by Roger Federer in 2009. He reached at least one Grand Slam final for 11 consecutive years, a record for a male player since equalled by Pete Sampras.

Lendl first attained the World No. 1 ranking on February 28, 1983, and bolstered his claim to the top spot when he defeated John McEnroe in the 1985 US Open final. For much of the next five years, Lendl was the top ranked player until August 1990 (with a break from September 1988 to January 1989 when Mats Wilander was at the top). He finished four years ranked as the world's top player (1985–87 and 1989) and was ranked World No. 1 for a total of 270 weeks, breaking the record previously held by Jimmy Connors (this has since been surpassed by Pete Samprasand more recently by Roger Federer).