Jefferies, who was nicknamed DJ by the fan scene and the trade press from his initials , came from a family of racing drivers. His father Tony Jefferies won the Isle of Man TT in the 1970s . His father Allan Jefferies was already a successful trial driver in the 1930s . And his uncle Nick Jefferies also won the Isle of Man. He started riding motorcycles at the age of seven; From the age of fourteen, DJ took part in the first motocross races. From 1990 he switched to street racing. In 1993 he won the British Superstock 1000 Championship. In 1993 he took part in both the 500cc motorcycle world championship and the superbike world championship . However, this with rather moderate success. He shifted his activities to road racing. From 1996 he took part in the TT, which he won nine times. Jefferies was the first rider to achieve a lap average of over 200 km / h in the TT. Jefferies had a fatal accident during training for the TT on May 29, 2003. He fell on an oil trail at over 200 km / h and hit a wall on the edge of the racetrack. With a body weight of 88 kg, Jefferies was actually considered too heavy for world-class racing. It was said that his weight resulted not only from his height of almost 1.90 m, but also from his great zest for life. For the centenary of the Tourist Trophy 2007, DJ was honored with a 100 pence stamp from the British Post.