Bernie Sanders is an incumbent US Senator from Vermont and is the longest-serving independent candidate in the history of the US Congress. He was a House representative from Vermont for 16 years (1991-2007) and has been a US Senator since 2007. It was not before 2015 that he gave up his independent status and joined the Democratic party

Age: 74 (born September 8, 1941)

Campaign: Bernie 2016

Main political views: Sanders calls himself a socialist, a rather uncommon label in American politics. He is inspired by the Scandinavian welfare model and is part of the more progressive left-wing in the Democratic party.

Chances of winning: Sanders seems to be the greatest and maybe only realistic challenger to the clear favorite Hillary Clinton for the Democratic nomination. Sanders is very popular among especially young voters, but he might be too left-wing to gain enough votes in the general election should he win the nomination. Thus, Clinton is regarded as the safer bet among many Democratic voters, when it comes to picking a candidate who can win the general election.

Update: Sanders surprised most people by staying in the race to the end, he eventually lost to Clinton, but did start a movement in the US that might help the Democrats win a majority in Congress in 2016.

(Photo credit: Gage Skidmore)