I is a letter used in almost all modern Cyrillic alphabets with the exception of Belarusian, where it is replaced by І.
И, from Alexandre Benois' 1904 азбука.
In early Russian typewriters like this one, there was no key for the digit 1, so the capital І was used instead. Following the Russian alphabet reform of 1918, a 1 key was added.
Short I or Yot/Jot or I with breve, Russian: и с бреве is a letter of the Cyrillic script. It is made of the Cyrillic letter И with a breve.
Yot, from Alexandre Benois' 1904 alphabet book
Contrastive use of Cyrillic kratka (for consonant [j]) and Latin breve (for short vowel [ĭ]) above и in Russian-Nenets dictionary