Odo of Rheims
"Odo was abbot of Saint-Remi in Rheims from 1118-1151. He claims to have been present when the mysterious John arrived in Rome and gave his narrations to Pope Calixtus II, as described in [De Adventu]. The De Adventu and this letter narrate the same event, but seem to be textually unrelated, which suggests that John's visit to Rome was a real occurrence, though little more can be said without dangerous excursions into speculation." (p. 41)