Saint John in Silence
As is typical in Orthodox icons, John is portrayed as a balding old man with white hair. The eagle on the left is his usual attribute.
The Hermitage Museum provides a page on another "Saint John in Silence" icon that explains this one quite well:
[It] depicts the apostle touching his lips with his right hand, as a sign that he is keeping silence, while with his left hand he points to the text of the Gospel According to St John. The size of the figure is exaggerated in comparison with the small angel behind the saint's shoulder. The hovering angelic form with a seven-pointed halo is an embodiment of the Holy Spirit, and symbolizes wisdom.
Read more about St. John the Evangelist.
Source: Wikimedia Commons