Lullus (born about 710 in Wessex, died 16 October 786 in Hersfeld) was the first permanent archbishop of Mainz, succeeding St. Boniface, and first abbot of the Benedictine monastery at Hersfeld.

His name is the latinized form of Lul, a short version of Germanic names that begin with the syllable "Lud" or "Lut" (e.g., Lutger, Ludwig). He was monk in the Benedictine monastery Malmesbury in Wiltshire. During a pilgrimage to Rome in 737 he met St. Boniface and decided to join him in his missionary work in northern Germany. In 738, Lullus joined the Benedictine order and the monastery of Fritzlar, founded by Boniface in 732, where abbot St. Wigbert was his teacher. He became deacon in 740, and was ordained priest by Boniface in 747. In 752 he became auxiliary bishop under St. Boniface. King Pippin confirmed him one year later as bishop of Mainz, so that Lullus became Boniface's successor after the latter's death in 754. Lullus became the first regular archbishop of Mainz when Pope Hadrian I granted him the pallium in about 781. He then greatly expanded his bishopric by absorbing those of Büraburg (near Fritzlar) and Erfurt.

From 769 onward, Lullus promoted the establishment of the monastery at Hersfeld, which he succeeded in having placed under Charlemagne's protection in 775.

Lullus' chief accomplishment was the completion of St. Boniface's reform of the church in the Frankish Empire and the successful conclusion of the Christianization of the Germans in Hesse-Thuringia. But while Boniface had looked for a close link to Rome, Lullus sought a better understanding with the Frankish kings.

Lullus died on 16 October 786 in Hersfeld where he was buried. He was canonized on 7 April 852.