Symeon (Hebrew Shimon) was — per the unanimous tradition preserved by the 2nd-century Christian historian Hegesippus (see his entry below) and reproduced by Eusebius — the son of Clopas (Cleophas, the brother of St. Joseph; see Mary of Cleophas in the 1st-c. supplemental catalogue), making him a first cousin of the Lord. He succeeded his other cousin James the Just (also called James the brother of the Lord) as the second Bishop of Jerusalem after James's martyrdom around AD 62.
He governed the Jerusalem Christian community for some forty-five years through the catastrophic period that included the Roman destruction of the Temple in AD 70 (the Jerusalem Christian community, under his direction, evacuated to Pella in the Decapolis before the Roman siege began — a foundational episode in the historical separation of Christianity from Temple Judaism). The Pella community returned to Jerusalem after the war and was the principal Jewish-Christian community of the Holy Land through the late 1st and early 2nd centuries.
Hegesippus records (preserved by Eusebius, Church History 3.32) that Symeon was denounced to the Roman provincial authorities around AD 107 as both a Christian and a Davidic-descent claimant to the throne of Israel — a politically sensitive accusation during the reign of Trajan, who had ordered the systematic execution of any surviving Davidic-line claimants. After prolonged torture he was crucified at the age of approximately 107 years (per Hegesippus's testimony — though some scholars regard the extreme age as a symbolic acknowledgment of his long ministry rather than literal biographical fact).