The MotoGP World Championship has produced timeless champions since its inception in 1949, and here is a list of the 10 greatest riders:

Kenny Roberts

He was the youngest person to have won a MotoGP premier class championship in his first year participating in the event. He was also the first American to win a world title in the 500cc motorcycle championship. From 1978 to 1980, Kenny Roberts won three MotoGP titles. His riding style was very influential and made him one of the greatest riders of all time. He was the first rider to pull off the cornering method of hanging off the motorcycle with his knees extended, which lead to major changes in how the motorcycles were ridden in GP races.
 

Marc Márquez

Marc Marquez has already made an indelible impression on the sport. Turning professional in 2010 at age 17, Marquez won the MotoGP title that year, followed by another title in 2012, and two back-to-back premier class MotoGP titles in his first two years as a professional racer, making him the youngest ever to accomplish that many wins. 

John Surtees

A great British racer in every respect. Surtees dominated the motorcycle racing sport during the 1950s. In addition to being a four-time World Champion in the 500cc motorcycle category,  Surtees also won three titles in the 350cc class, giving him a total of seven world titles in motorcycle racing. However, John Surtees was not just a bike racer. He also raced cars and competed in Formula 1 GP races.
 

Mike Hailwood

“Mike The Bike,” as Hailwood was known, is the other British motorcycle rider who challenges John Surtees in the debate for greatest racer of all time. Hailwood dominated the sport of motorcycle racing between the years of 1958 and 1967, winning a total of four world championships, and nine championships in different motorcycle classes.

Michael Doohan

Australian rider Michael Doohan is considered one of the greatest motorcycle riders of all time. He won five back-to-back MotoGP titles between 1994 and 1998. Michael Doohan was more than your typical motorcycle rider. He had a knack for setting up his bike and had a great insight into the 500cc class of motorcycles. Many people consider Michael Doohan to be a mechanic as much as a rider.

Casey Stoner

Although he retired relatively young and only won two world championships, Australian racer Casey Stoner is considered to be one of the greatest motorcycle drivers in history. A two-time MotoGP World Champion in 2007 and 2011, Casey Stoner was known for his ability to ride any motorcycle beyond its limits. Stoner was well known for having exceptional control of the bike he drove, even at breakneck speeds.

Wayne Rainey

One can say he is the best American bike racer of all time, Wayne Rainey dominated the sport in the late 1980s and early 1990s, winning the MotoGP World Championship three times and the Daytona 200 once. Wayne Rainey was praised for his smooth racing style and cool demeanor. Rainey likely could have won more championships if he was not in an accident in 1993 that ended his career.

Jorge Lorenzo

MotoGP is arguably the most popular in Spain, and there, everyone knows the name, Jorge Lorenzo. Being the MotoGP World Champion in 2010, 2012, and 2015, Lorenzo is like royalty in his native Spain. He began his professional career at the age of 15 and has been a sensation ever since.

Valentino Rossi

The living Italian legend announced his retirement at the end of last season and is the only rider in history to win world championships in 125cc, 250cc, 500cc, and MotoGP. He won his first Class A title in 2001 at the age of 22, the first of five consecutive championships - with Honda and then with Yamaha. He won two championships later in 2008 and 2009. He is the only rider to have started 400 or more races in the history of the sport, and has 89 first-class victories...nobody in the history of Grand Prix racing has come close to that.

Giacomo Agostini

Italian rider Giacomo Agostini is considered the greatest motorcycle race driver of all time. During his career from 1964 to 1977,  Agostini tallied 122 GP wins and 17 World Championship titles, most of them in the 500cc class. Although seven of his world title wins were in the 350cc class of bikes, the 17 championships make Agostini the most successful rider on two wheels ever. Agostini is a legend and ambassador for the sport of MotoGP.