Ioannes I (Greek: Ἰωάννης A΄, "John I") may refer to:
- Patriarch John I of Constantinople (c. 347–407)
- John I Tzimiskes (c. 925–976), Byzantine Emperor
- John I Doukas of Thessaly (c. 1240–1289)
See also
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Ioannes I (Greek: Ἰωάννης A΄, "John I") may refer to: