Complex sentence: Symmachus the Ebionite (fl. late 2nd century) was the author of one of the Greek versions of the Old Testament that were included by Origen in his Hexapla and Tetrapla, which compared various versions of the Old Testament side by side with the Septuagint.
Split into simpler sentences: Symmachus the Ebionite (fl. late 2nd century) was the author of one of the Greek versions of the Old Testament. It was included by Origen in his "Hexapla" and "Tetrapla", which compared various versions of the Old Testament side by side with the Septuagint.