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.

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 § Criminal record).

Leonard Roscoe Tanner III[5] hailed from Lookout Mountain, Tennessee, graduated from Baylor School[6] in Chattanooga, and with teammate Sandy Mayer helped to lead Stanford University's rise to national prominence in collegiate tennis.

Tanner defeated Guillermo Vilas in three straight sets in the 1977 Australian Open (January) final, to win his first and only grand slam title.

Tanner described his 1979 US Open win over Borg and loss to Gerulaitis in his autobiography as "the highest of my highs and the lowest of my lows on a tennis court within two days of each other".

[2] Tanner's unorthodox but very strong left-handed serve was tossed very low and struck with a lunge involving the whole body, earning him the nickname "The Rocket".

[13] In March 2013, Tanner was arrested in Florida for writing a bad check and grand theft, and in 2014, he served 10 days for driving with a suspended license.