The sagas depict Sumarlidi as a wise, quiet and peaceful man. More is not told about him, other than that he died of illness in his bed only shortly after he became earl. After he was gone, there was a quarrel between Einarr and Thorfinn about who would inherit his part of the earldom.
References
Anon., Orkneyinga Saga: The History of the Earls of Orkney, tr. Hermann Pálsson and Paul Edwards. Penguin, London, 1978. ISBN0-14-044383-5