Grace O'Malley, is an important figure in Irish legend but was in fact a larger-than-life figure from 16th century Irish history.  

One of the most enduring legends about her dates from this period and concerns Howth Castle, which still stands some ten miles from Dublin City. Returning from a voyage, she put in to the port of Howth for provisions. Granuaile duly went to see the local lord, St Lawrence, to seek his hospitality, as was the Gaelic custom. She found the castle gates locked and was told by the servants that his lordship was at dinner and would not be disturbed. Heading back to her ship she came upon St Lawrence’s young grandson playing in the grounds, kidnapped him and took him back to Clew as her hostage. Convinced the ransom would be high, Howth opened negotiations for the boys’ return. Gráinne contemptuously dismissed his offers of gold and silver. Her price, she declared, was that the gates of Howth Castle must never again be locked and that an extra setting must evermore be laid at the dinner table, lest an unexpected guest should happen to stop by. Relieved at the simplicity of the demand, St Lawrence agreed and returned to Howth with his grandson, where he faithfully kept his side of the arrangement and where, even today, the castle gates are always open and an extra place laid at the dinner table in commemoration of the family’s legendary encounter with the Pirate Queen

James Joyce used the legend of Grace O'Malley ("her grace o'malice") and the Earl of Howth in chapter 1 of Finnegans Wake, but added the kidnapping of another fictional son, Hilary, to match his Shem and Shaun theme. Christopher/Tristopher is turned into a Luderman (happy Lutheran) and Hilary into a Tristian (sad Christian).