23 April is St.George‘s Day commemorating the circa 303AD death of this mythical knight and dragon slayer. Catholic (and Anglican) calendars traditionally move their memorial Feast day to the first Monday after Easter Week.
William Shakespeare (1554-1616) died this day, and was born on (or just before) this day. This day is also known as Georgemas. UNESCO celebrated the yearly World Book Day for the first time in 1995.