Irish author James Joyce begins a relationship with Nora Barnacle and subsequently uses the date to set the actions for his novel Ulysses; this date is now traditionally called "Bloomsday" in honour of the novel's main character Leopold Bloom #OTD in 1904.
The first mention of such a celebration is to be found in a letter by Joyce to Miss Weaver of 27 June 1924, which refers to "a group of people who observe what they call Bloom's day – 16 June." via @Wikipedia
