Eleuterus (Greek Eleutheros, 'free') succeeded Soter around AD 174 and governed the Roman community for some fifteen years through the late reign of Marcus Aurelius and the early reign of Commodus. The Liber Pontificalis attributes to him the substantial 15-year ministry.
He is connected — at least in the late-medieval Catholic tradition preserved by the Liber Pontificalis and the Venerable Bede — with the foundational legend of Catholic British Christianity: that a British king named Lucius (Lleirwg, in Welsh tradition) wrote to Eleuterus around AD 180–189 asking that missionaries be sent to convert his kingdom to Christianity, and that Eleuterus accordingly dispatched the missionaries who established the first British Catholic dioceses. The historical reliability of the Lucius of Britain tradition is contested; modern critical scholarship is sceptical of its historicity, though the tradition was substantially developed across the Middle Ages and used as foundational for the Welsh and Anglo-Saxon Catholic identity.
Eleuterus also had to deal with the rapidly intensifying Montanist crisis from Asia Minor (see the Apollinaris of Hierapolis entry above for the Montanist movement). Eusebius records (Church History 5.4) that the Christians of Lyon — including the Pothinus and Blandina group that would be martyred shortly after under Marcus Aurelius (see their entry in the 2nd-c. catalogue) — sent a letter to Eleuterus during their persecution recommending Irenaeus to him as their messenger and asking him to maintain ecclesial-doctrinal moderation in dealing with the Montanist controversy.