The 2012 Formula 1 season will have a record six current or former World champions on the grids.Altogether, the six have collected 14 titles, led by record champion Michael Schumacher with seven. The others are double winners Sebastian Vettel and Fernando Alonso; Lewis Hamilton, Jenson Button and Kimi Raikkonen have each won one Drivers' title.Here's a review of the champions:Michael Schumacher: The German will compete in his 300th F1 race this season. The 43-year-old is the veteran of the field but, with seven titles and 91 GP wins, he is also by far the most successful driver in F1 history. Schumacher returned in 2010 from a three-year F1 break and has not won a race since. It's unknown whether he will continue as a Mercedes driver at the end of his three-year contract.Sebastian Vettel: This young German is eyeing a hat trick. If the 24-year-old gets a third consecutive World title he will become the youngest driver to do so. The only two drivers with a similar record were Juan Manuel Fangio in the 1950's (four in a row) and Michael Schumacher at the start of the millennium (five in a row). Vettel is clearly the driver all others are chasing.Fernando Alonso: The Spaniard was once in Vettel's shoes as the youngest double champion (2005 and 2006) with Renault. He joined McLaren for a year then returned to Renault and then on to his "dream team", Ferrari, in 2010. He only won one race in 2011.Jenson Button: The Briton was World champion in 2009 and runner-up in 2011. He seems very relaxed going into 2012, just like always. Button seems at peace with himself and the world around him. He is not a track rowdy and not one to do a lot of talking off it. The 32-year-old will once again be a challenger to Vettel this season.Lewis Hamilton: The Briton would do anything to add another World title to his 2008 success; a personal drive that was often his problem in a 2011 season full of accidents, fines and failures for the 27-year-old. Hamilton did nothing to correct his gung-ho style and had relationship problems off the circuit. All told, it was a tough 2011 for him. Things can only get better.Kimi Raikkonen: The Finn was fastest in the first test and the final test of 2012 but can the 32-year-old really be considered a title contender? The Iceman has not really changed at all. He still doesn't talk much and when he does it's usually incomprehensible but he's hoping to have the World champion's trophy back on his shelves; it was there in 2007.