Ben Carson (63):The retired neurosurgeon is most renowned for his breakthrough work in separating conjoined twins. He was awarded the Presidential Medal of Freedom in 2008, he's written six books and has had a TV film made about his life.

Carson has been baptised twice into the Seventh Day Adventist Church, and writes in his 2008 book Gifted Hands that "The Adventist denomination is the only spiritual home I've ever known."

At his official campaign launch in his hometown of Detroit on May 4, which featured a gospel choir, he told the crowd: "I'm probably never going to be politically correct, because I'm not a politician. I don't want to be a politician because politicians do what is politically expedient, and I want to do what's right." Carson only joined the Republican Party in 2014.

His reputation for being outspoken, and at times controversial, has earned him the love of some conservatives – particularly after he slammed Obamacare at the National Prayer Breakfast.

He's critical of political correctness and defends the right to religious freedom. In his 2012 book America the Beautiful he writes: "Today the forces of political correctness would expel God from every public sphere in American life, and the hearts and minds of every man, woman, and child in America are up for grabs in this cataclysmic battle between the lovers of men and the lovers of God... I believe it is time for us to stand up and be counted."

He's also spoken widely of his pro-life stance and belief in 'traditional marriage'. In an op-ed for the Washington Times last year he wrote that "Attempting to characterize love and compassion for human life as a 'war on women' is deceitful and pathetic. We the people must stop allowing ourselves to be manipulated by those with agendas that do not include regard for the sanctity of life."

Speaking of his personal faith in an interview with CBN he said: "The most important thing for me is having a relationship with God. To know that the owner, the creator of the universe loves you, sent His Son to die for your sins, that's very empowering."

But although he appeals to the Christian vote in some respects, he isn't guaranteed support from Southern Baptists. Having been invited to speak at the Southern Baptist Pastors' Conference in June this year, he has now had to withdraw from the event after the conference president Willy Rice faced criticism for appearing to endorse a candidate, particularly one who was not a Southern Baptist, according to the Christian Examiner.