Casey Stoner will be a hard rider to beat over the next five years as he strives to match the race records of Giacomo Agostini and Valentino Rossi,.Five-times World champion Mick Doohan said Stoner won his first of MotoGP title in 2007 with Ducati and switched back to Honda for in 2011 to claim his second championship.'ONE OF THE BEST'Doohan, who spent his entire 500cc career with Honda, spoke to Reuters at a Laureus event ahead of this weekend's season-ending Valencia MotoGP."Honda's a more stable platform," Doohan said. "If they get the bike right again in 2012 he should keep winning. He understands the bike. If the bike stays there I think over the next five years it's his to lose. He's going to be a hard guy to beat."Already, on paper, he's one of the best there's been."Doohan won five titles in a row before an injury ended his career in 1999.Agostini, motorcycling's most successful rider, won eight titles in the top category between 1966 and 1975. Rossi is second on the list with seven.Doohan said: "If Stoner consolidates the 2011 championship with another one he's just going to get bigger and bigger. He's already a household name, the only big difference is that people probably wouldn't know his face."He's just racing bikes. Winning races is what he's contracted to do. He's a quiet guy. Just because you're a World champion doesn't mean you have to be a movie star."DEATHS IN MOTOGPMotorcycling has long been known for its flamboyant characters, one of whom, Italy's Marco Simoncelli, was killed when his bike slid into the path of Valentino Rossi and Colin Edwards during the October, 2011 Malaysian MotoGP in Sepang.It was the first death in the sport's premier category since Japan's Daijiro Kato in 2003, and occurred a week after Britain's double Indy 500 winner Dan Wheldon perished in a fiery crash at the Las Vegas Motor Speedway.Doohan found the subject a difficult one to talk about and said he felt it was important to be in Spain for the final race, where Stoner has promised to honour Simoncelli with some exciting racing.Doohan commented: "It's not up to me to comment. It's such a personal thing. It's somebody's life, it's somebody's family and son. Following what's happened, I think it's a good time to show up."The week after (Formula 1 driver) Ayrton Senna's death (in 1994) was a similarly bad time. Thankfully it doesn't happen often."Doohan said: "There's always going to be controversy. Football and rugby kill people, too. Are we going to ban all sports? Life is terminal. We could all sit in the lounge and not get off our butt but that's not the nature of what we are."It was a grim week for motorsport but all we can do is try and learn from it and try and improve."MotoGP and IndyCar officials have launched investigations into the two tragic incidents as motorsport, on two wheels and four, faces its greatest safety inquest for a generation.