He was bishop of Ravenna, probably in the late second century, and was probably martyred there. Devotion to him was already common in the seventh century.
Prayer from Morning Prayer:
God of power and mercy, you gave Saint Apollinaris, your martyr, victory over pain and suffering.
Strengthen us who celebrate this day of his triumph
and help us to be victorious over the evils that threaten us.
Grant this through our Lord Jesus Christ, your Son,
who lives and reigns with you in the unity of the Holy Spirit,
one God, for ever and ever.