Mathea Ager, née Fredrikke Marie Mathea Johnsdatter Stillaugsen, was born in 1835 in Fredrikstad, Norway, to John Stillaugsen of Onsø, a sailor. She married Martinius Mathiesen Ager, with whom she had several children, of whom three survived to adulthood: Camilla, Waldemar and Johan. She died on Christmas Day, 1913, and is buried in Chicago.

Mathea worked as a seamstress and was described by a Methodist pastor who knew her as "one of the most unusual women I have met in my life." Others said that she was intelligent, well read and a good storyteller.