The second deputy prime minister has been in politics for more than two decades, and has served as a running mate to both frontrunners in previous elections.
He started off as a member of parliament in 1989, and later become minister for finance. He had a short stint as the nation's vice president more than a decade ago.
The 52-year-old former rugby player is a contender for the Amani Coalition. He graduated from the University of Nairobi.
The veteran politician's win would make her the first female president in Kenya. She was a big part of the current government, but cut ties with it four years ago when she resigned as justice minister.
A former lawyer, the 55-year-old Karua has said if she doesn't win the presidency, she will retire from politics.
She equates her leadership to that of a mother, and has said she will run the government like a household and not let her children go hungry.
Her campaign slogan is "Simama na Mama," which translates to "Support Mom" in Swahili.
The University of Nairobi alumna is a contender for the National Rainbow Coalition-Kenya party.
Four others are running, including former banker Peter Kenneth, Mohammed Dida, Paul Muite and James Ole Kiyiapi.