Frederick (died October 954) was the Archbishop of Mainz from 937, following the late Hildebert, until his death.
In 939, he joined the rebellion of Eberhard III of Franconia, Gilbert of Lorraine, and Henry I of Bavaria.
He plotted with Henry to assassinate Otto in Easter 941 in Quedlinburg, but they were discovered and put in captivity in Ingelheim, being released and pardoned only after doing penance at Christmas of that year.
Frederick refused to accompany Otto to Italy in 951.
Abandoned by the Lorrainers and without Henry's support this time, the rebels were easily crushed and punished.