Alonso made his F1 debut for Minardi in 2001 before joining Renault as a test driver in 2002.
The Spaniard's 2005 title ended Michael Schumacher's five-year reign and made him then the youngest world champion in F1 history at the age of 24 years and 59 days. He retained his title the following year.
Alonso endured a tumultuous and often acrimonious season alongside Lewis Hamilton at McLaren in 2007 before a brief return to Renault followed by a four-year stint with Ferrari from 2010. He joined McLaren in 2015.
Alonso's focus is now on capturing motor sport's fabled "Triple Crown" of victories at the Monaco Grand Prix, the 24 Hours of Le Mans race and the Indianapolis 500.
He's won in Monaco in both 2006 and 2007, while he was part of TOYOTA GAZOO Racing's victorious team at Le Mans earlier this year. An attempt to win the 2017 Indy 500 finished with just 21 of the 200 laps remaining.
"I achieved much more than what I dreamed of when I started," says Alonso. "I think it's the right time now because there are some other challenges out of Formula One that I'm very, very interested in now.
"My idea is to win all the iconic motor sport races in the world."
'Everything in life is a competition'
Indeed, winning is the thing Alonso loves more than anything.
"Winning is everything," he says.
"Not only (in) sport, but in life. In life, it's winning -- when I go to the supermarket and I go with a friend, I try to get through the door first.
"Things like that, everything in life is a competition for me."
Alonso won his last F1 grand prix in Spain while driving for Ferrari in 2013, but despite a lack of success with McLaren he says the team is on the right track.
"I still believe that McLaren is one of the best teams in history of the sport, and they will get better eventually in a couple of years time," he says.
He added: "I miss winning. I miss being on the podium."
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