Former MotoGP champion Nicky Hayden has died aged 35, five days after being involved in a crash while cycling.
The American suffered "serious cerebral damage" after colliding with a car on the Rimini coastline in Italy on Wednesday, 17 May.
The 2006 MotoGP championship winner had been in the intensive care unit of Cesena's Maurizio Bufalini Hospital.
"We would like everyone to remember Nicky at his happiest - riding a motorcycle," his brother Tommy said.
A hospital statement issued on Thursday said Hayden had suffered "a serious polytrauma", which is a medical term to describe the condition of a person who has multiple traumatic injuries.
Hayden, who was nicknamed the Kentucky Kid, had competed for Red Bull Honda in the World Superbike Championship in Italy on 14 May.
Older brother Tommy, who was also a motorcycle racer, said the family had many "great and happy memories" of Hayden.
"He dreamed as a kid of being a pro-rider and not only achieved that but also managed to reach the pinnacle of his chosen sport," he said.
- From the archives: Hayden claims shock world title
- The backyard racer who conquered the world
- Toseland: Hayden the nicest MotoGP rider ever
"We are all so proud of that. We will all miss him terribly."
Sister Kathleen added: "Today I not only lost my big brother, but I lost a best friend."
Red Bull Honda World Superbike said that the racing world had said goodbye to "one of its dearest sons."
"The 'Kentucky Kid' will be sorely missed by all that ever had the pleasure of meeting him or the privilege to see him race a motorcycle around a track, be it dirt or asphalt," a statement read.
Hayden's title triumph
The Kentucky-born racer first competed in MotoGP in 2003 and finished third in the standings two years later. He ended Valentino Rossi's five-year winning streak in 2006 following a dramatic final race in Valencia.
Hayden had been eight points adrift of Rossi heading into the decider, but saw the Italian slide out on lap five and eventually finish in 13th place. Hayden's third-place finish allowed him to take the title by five points.
He remains the last American to win the premier class of motorcycle road racing.
At the time, BBC commentator Steve Parrish described the season as "the most entertaining I have ever seen".
'A champion and a gentleman'
'His family were such a huge part of who he was'
BBC's Azi Farni
Nicky was a real gentleman. He came from a wonderful family, a big racing family. His two brothers raced, his two sisters raced when they were younger, his father raced.
This was a dirt track family. They come from Kentucky and had a race track at their house. Racing was something that they all did together.
His family were such a huge part of who he was. If you look at his Twitter handle it says "bikes and family".
He was so loving and this is going to be such a great loss for them.