Rick Santorum is a former Senator from Pennsylvania and held the Republican party's third-highest position from 2001 to 2007.
His campaign strongly emphasises his traditional family values and his commitment to reducing the number of people on welfare benefits.
Most notable is his stance on Iran, which he believes to be a serious and immediate threat. Alongside funding for pro-democracy groups and publicising of its human rights abuses, he advocates:
"Work[ing] with Israel to eliminate the Iranian nuclear threat immediately; and developing a potential plan for military action if needed."
Santorum opposes what he calls 'frivolous lawsuits against the gun industry', saying that as a native of a state with a rich hunting and fishing industry, he understands the importance of the 2nd Amendment (the right to bear arms).
He also opposes Obama's health reforms and has vowed to repeal them if elected, replacing universal care with a 'market-driven, patient-centred solution'.
His fiscal policy includes freezing military spending to avoid any cuts for five years, in order to 'prioritise national security and defence.'
He wants to slash resources to the Environmental Protection Authority and the United Nations, and halve the staff of USAID.
He has also vowed to stop any remaining payout of the Obama administration's stimulus package.
Santorum has a history of offending the gay and lesbian community with comments like this one in 2003:
[Gay sex] destroys the basic unit of our society because it condones behavior that's antithetical to strong healthy families... In every society, the definition of marriage has not ever to my knowledge included homosexuality. ... It's not, you know, man on child, man on dog, or whatever the case may be. It is one thing.”
Gay rights activist Dan Savage struck back by turning his name into a neologism referring to anal sex, which became the top Google hit for any search of his name.
He petitioned Google to change the result, but Google refused.
Watch one of Rick Santorum's campaign ads:
