Leonard Roscoe Tanner is an American former professional tennis player. He reached a career-high singles ranking of world No. 4 on July 30, 1979.
Tanner won 16 titles throughout his career. Tanner was famous for his big left-handed serve, which was reportedly clocked at 153 miles per hour (246 km/h) at the Mission Hills Country Club in Rancho Mirage, California on February 19, 1978 during the 1978 American Airlines Tennis Games singles final against Raúl Ramírez.
He is also known for winning the men's singles title at the first of two Australian Open tournaments held in 1977. Tanner won the tournament held in January. Tanner reached the Wimbledon final in 1979, narrowly losing to Björn Borg in five sets.
After his retirement, Tanner received media attention in the 2000s for legal problems that included stretches of imprisonment, arrests for missing child support payments, allegations of financial misdeeds, and bankruptcy (see § Legal issues).