Complex sentence: Little is known of Theodore's background; he is recorded as being born a Roman, and the son of Photios I of Constantinople, who was the Patriarch of Constantinople, and his brother Theodosius (or Theosius) was also a bishop.
Split into simpler sentences: Little is known of Theodore's background; he is recorded as being born a Roman, and the son of Photios I of Constantinople, who was the Patriarch of Constantinople. His brother Theodosius (or Theosius) was also a bishop.