Aunt Ester, referred to in Two Trains Running and King Hedley II, is a central character in Gem of the Ocean. In the preface to King Hedley II, August Wilson wrote: "Aunt Ester has emerged for me as the most significant persona of the cycle. The characters, after all, are her children. The wisdom and tradition she embodies are valuable tools for the reconstruction of their personality and for dealing with a society in which the contradictions, over the decades, have grown more fierce, and for exposing all the places it is lacking in virtue."
There is a symbolic dimension in her reputed age, which makes her precisely as old as the first slaves brought from Africa to the Americas. Her home is at 1839 Wylie Avenue, a real address but one which signifies the year of the Amistad slave rebellion. (No building currently exists at that address, although as far as I know, what stood there before hasn't been researched.)
But there may be an historical ancestor to the character of Aunt Ester. The title of the play comes from the 19th century song"Columbia, Gem of the Ocean," which was about an actual ship, the Columbia Rediviva, the first American ship to circumnavigate the globe. By then, the figure of "Columbia" as a symbol of America, and a female one (counterposed to Columbus) was well known as well. According to the OSF guide to this season's plays, the latest scholarship suggests that Columbia was first used in this way by Phillis Wheatley, an ex-slave who became the first black poet living in America to publish a book of poems, in 1773.
I think she may also be something of a model for Ester Tyler. Both were taken from Africa and sold as slaves when young girls, both were domestic servants to white women, took their last names and stayed with them until their deaths. Both have first names with slightly unconventional spelling. There are differences, the most obvious being that Phillis Wheatley died at the age of 31.