Yo (Ё, ё) is the seventh letter of the Russian Cyrillic alphabet, invented to replace the recklessly confused е and o for soft o relatively soon after the introduction of the Civil alphabet.
It is used in the Russian and Belarusian languages, along with many of the Caucasian and Turkic languages which use or used the Cyrillic alphabet, but not in many of the other Slavic languages.
Yo is identical in form to ye, as well as Latin E, except for a symbol similar to an umlaut or diaeresis.
The original Cyrillic alphabet was a writing system developed in Bulgaria in the tenth century to write the Old Church Slavonic liturgical language.
Cyril, a missionary who, along with his brother, Methodius, is credited for inventing the Glagolitic alphabet, an earlier Slavic alphabet and an influence on this one.
Variations of the Cyrillic alphabet are used to write languages throughout Eastern Europe and Asia.