"Excelsior" is one of Sam Loyd's most famous chess problems, originally published in London Era in 1861.
It is not to be confused by a popular 1958 study of the same name by Russian chess composer Vladimir Korolkov, which has a similar thematic motif.
[1] Loyd had a friend who was willing to wager that he could always find the piece which delivered the principal mate of a chess problem.
Loyd composed this problem as a joke and bet his friend dinner that he could not pick a piece that didn't give mate in the main line (his friend immediately identified the pawn on b2 as being the least likely to deliver mate), and when the problem was published it was with the stipulation that White mates with "the least likely piece or pawn".
3... Bc7 4. cxb7 any 5. bxa8=Q/B# Any problem that features a pawn moving from its starting square to promotion in the course of the solution is now said to demonstrate the Excelsior theme.