Brain Snacks: Tasty Tidbits of Knowledge
Major Robert Gregory, the Irish airman on whom this poem is based, was a well-known cricket player back in the day (cricket is a British game, kind of like baseball). (Source.)
Yeats wrote four poems about Major Robert Gregory. Must have been an important friend of his. (Source.)
Yeats wrote the epitaph that appears on his own tombstone. It reads "Cast a cold eye / On life, on death. / Horseman, pass by!" They are the last lines of one of Yeats' final poems, "Under Ben Bulben." (Source.)
It turns out that maybe Yeats and Gregory had a little falling out before Gregory went off to war. Since he was the legal owner of Coole Park, where Yeats spent a lot of time, he could do whatever he wanted. He eventually evicted Yeats from the master bedroom, and barred access to the wine cellar. (Source.)