Euthymius I Synkellos (Greek: Πατριάρχης Ευθύμιος Α΄) was the Ecumenical Patriarch of Constantinople from 907 to 912. He came to the office after Emperor Leo VI forced Nicholas I Mystikos to resign over Nicholas' refusal to sanction the Emperor's fourth marriage.
The Vita Euthymii, or The Life of Euthymius, along with the correspondence of patriarch Nicholas and the writings of Arethas of Caesarea, is one of the main historical sources for the period.
| Preceded by Nicholas I Mystikos |
Patriarch of Constantinople 907 - 912 |
Succeeded by Stephen II of Amasea |