By Drazen Jorgic

ISLAMABAD (Reuters) - David Rudisha tore up the tactical script at the London Olympics to smash the world record in one of the greatest ever 800 meter runs and emerge as an athletics superstar to rival the sport's biggest names.

For Kenya's "King David" to cement his Olympic legacy by becoming the first man to successfully defend his title since the 1964 Olympics, however, he will need shake off doubts about his form and mental fortitude after a mediocre season.

Rudisha finished third in the Kenyan trials and his Diamond League form has been poor. His mentor and coach, Brother Colm O'Connell, last month questioned Rudisha's mental toughness and said he had "done very very little training" with him in 2016.

Few expect Rudisha, who hails from Africa's Maasai tribe, to dent the world record of 1:40.91 set in London, the zenith of his illustrious career.

Yet it would be foolish to write him off after he snatched his second world title in Beijing last year after a similarly off-color season.

"I feel that my body is coming back pretty nicely and I am in better form than last year. I am focused and determined to defend my title," Rudisha said after the Kenyan trials.

A Rudisha victory would go a long way toward lifting Kenyan spirits after the African nation's pristine reputation was tarnished by a spate of doping scandals that at one point threatened the country's participation at Rio.

Rudisha's beaming smile and the manner of his 2012 victory, which his childhood hero and now IAAF President Seb Coe described as "the most extraordinary piece of running I have probably ever seen", catapulted him to global stardom.

"Bolt was good, Rudisha was magnificent," Coe said after the stunning 2012 race, in which all eight athletes beat the gold-winning time set at the 2008 Beijing Olympics.

O'Connell, an Irish missionary who first spotted Rudisha as a 14-year-old, told Reuters back in October that Rudisha had achieved riches and fame and was now motivated by the prospect of "greatness".

By the time of the Kenyan Olympic trials last month, however, O'Connell hinted at discord within the camp.

"Although I know he is a very experienced athlete, I am not sure if he is mentally fit. It would be misleading to say I knew his mental or physical strength. He has not been in touch for a long time," said O'Connell.

Rudisha afterwards referred to O'Connell as his "coach" on Twitter, refuting claims the two had split.

But in Kenya's running heartlands there have been doubts voiced about Rudisha's ability to replicate the type of form that saw him shine in London.

Rudisha has always been clear: he prefer medals over records, which are inevitably improved with previous holders forgotten.

"There is nothing more special than winning the Olympics. That is something that you will be remembered for entire life and for many generations to come," Rudisha said last year.

(Editing by Nick Mulvenney)