Peter Lundgren, who was a former professional tennis player from Sweden, died at the age of 59.
He was one of the first coaches that Roger Federer used when he was still young.
His son Lukas said that his father had left us too soon.
During the 1980s, he was part of a generation of Swedish players that were following in the footsteps of Bjorn Borg.
Borg, who was a professional player for many years, paid tribute to Lundgren, who was known for his large heart and sense of humor.
At the peak of his career, he was ranked 25th in the world.
After retiring from tennis, he went on to coach Roger.
He helped the Swiss player win a total of 10 ATP titles.