The Irish saint Fursa (d. 649) is renowned for his visions of the otherworld, transmitted in a near-contemporary Vita. He also appears in the Irish martyrologies and genealogies, the latter attributing to him a variety of pedigrees on his father's as well as his mother's side. This paper aims to show that by combining evidence from different types of sources; biographies, genealogies (Corpus genealogiarum sanctorum Hiberniae and Corpus genealogiarum Hiberniae), martyrologies (Félire Óengusso, Martyrology of Donegal and Martyrology of Cashel), and several Irish saints' Lives, it is possible to single out the most probable strand of tradition for the saint's origins. As it turns out, Fursa's differing genealogical affiliations mirror the subsequent shifts in political and ecclesiastical developments in Irish medieval history. Viewed from this perspective, the genealogies can supply valuable source material necessary for a biographical approach to a personality of the early Middle Ages.