Polls show that Bachelet, 61, is the runaway favorite in the race, even though she first has to win a June primary election against three largely unknown candidates.

The ex-president arrived in Santiago late Wednesday after three years living in New York, where she became the first head of UN Women, an office that supports the rights of women worldwide, when it was created in 2010.

“We knew there were things still to be done” when her coalition left office, Bachelet said, “especially to improve the levels of income disparity.”

A socialist, agnostic, single mother, Bachelet was a strange choice to lead staunchly Roman Catholic Chile, but her informal political style and personal touch led her to being dubbed “the mother of Chileans.”

She left office with an approval rating of 84%, despite criticism over the response to Chile's massive February 2010 earthquake, and left behind a legacy of mostly successful efforts to improve the lot of Chilean women.

Born in September 1951 in Santiago, Bachelet studied medicine and joined the Socialist Youth as a teenager. Her father, an Air Force general, was a close adviser to president Salvador Allende, and was imprisoned and tortured after Augusto Pinochet toppled the socialist leader on September 11, 1973. Bachelet's father died six months later.

Secret police whisked Bachelet and her mother to a torture center in January 1975. The two women were eventually freed, and fled first to Australia and then to East Germany, where Bachelet completed her medical studies.

Bachelet, already the mother of a young son, returned to Chile in 1979 but was prevented from practicing as a doctor by the dictatorship. She continued studying specializing in pediatrics and public health and in 1984 gave birth to a daughter. Her third child, Sofia, was born nine years later.

Bachelet studied military strategy in Santiago and later in Washington, and in 2000 was appointed health minister with a mandate to reform the sector. She later became Minister of Defense.