MIAMI (AFP) — Nick Bollettieri, the celebrity tennis coach who helped develop such icons such as Andre Agassi and Monica Seles, died on Monday aged 91.

While his methods were sometimes controversial, his academy in Florida churned out top players. Agassi, Maria Sharapova, Seles, Jim Courier, Anna Kournikova and Mary Pierce all passed through his Bradenton complex.

Bollettieri also advised Venus and Serena Williams and Boris Becker.

The demanding routine for children and adolescents living and training at his academy produced results but also drew criticism. His relationship with some of his successful proteges, including Agassi and Seles, eventually soured.

"I hated it at Bollettieri's academy," Agassi said.

"The only way I could get out was to succeed."

Bollettieri, though, remained unrepentant.

"I did what had to be done. Tennis is not a sport for choirboys," Bollettieri said.

Bollettieri was born in Pelham in the New York suburbs on 31 July 1931. He studied philosophy at a small Catholic college in Alabama, saying later that was when he started playing tennis regularly.

After serving in the US Army in Korea, Bollettieri started a law degree in Miami but dropped out to become a professional tennis coach.