Frederik Løchte Nielsen (born 27 August 1983) is a professional tennis player. He is currently the top ranked player from Denmark in ATP doubles world rankings. A former Wimbledon men's doubles champion, he peaked at no. 17 in the rankings in April 2013. Nielsen has reached five other doubles finals on tour, winning on two occasions.
Nielsen's parents were both tennis players and he began playing tennis at the age of three. Having turned professional in 2001, he began competing on the ITF circuit, winning a singles title every year between 2005 to 2010. He continued to play in ITF and ATP Challenger tournaments, garnering considerable success on the double circuit where he won multiple titles during the period.
Nielsen made a transition on to the main ATP Tour beginning 2012. He represented Denmark at the Hopman Cup that year, playing some tight matches against top-ranked opponents including Tomas Berdych and Mardy Fish, while also winning in doubles with Caroline Wozniacki. Nielsen entered the 2012 Wimbledon Championships with Jonathan Marray as wildcard entrant, but the duo went on to win the tournament upstaging such higher-ranked opponents as the Bryan brothers en-route to the title. He became only the second Danish player to ever win a Grand Slam and the first wildcard entrant to win Wimbledon men's doubles title.