What was Djokovic's career-high ATP singles ranking?

Novak Djokovic’s career-high ATP singles ranking was No. 1.

He first reached the top spot on 4 July 2011, after winning Wimbledon for the first time. That breakthrough ended the long-standing dominance of Roger Federer and Rafael Nadal at the summit and confirmed Djokovic as the leading player of his generation.

“Career-high ranking” means the highest position a player has reached, not necessarily the position they hold today. Djokovic has returned to No. 1 repeatedly and has spent more weeks there than any other men’s singles player. He has also finished a record number of seasons as year-end No. 1.

This answer is sometimes confused with his ranking during a particular tournament or season. No. 4, No. 3, and No. 2 have all been positions associated with Djokovic at various times, but none is his peak ranking.