Many reference works for music—and presumably other topics—contain articles about fictitious characters. Sometimes writers for these works slyly slip them by their editors (an article on “Verdi, Lasagne” was almost typeset for printing in The new Grove dictionary); others are incorporated with the collusion of all parties.
For an example, look up Otto Jägermeier in Komponisten der Gegenwart (available through RILM music encyclopedias) or in Die Musik in Geschichte und Gegenwart (available through MGG Online). You will find that Jägermeier composed, among other intriguing works, an opera called Der Idiot with a libretto by Fëdor Dostoevskij, and a work for solo clarinet called Psychosen. The name Jägermeier is a play on Jägermeister, a popular German cordial (above).
RILM is not above adding a spoof article or two to its database. Of course we won’t tell you which ones they are, but we’ll give you a hint: One includes a reference to the very real and wonderful Malcolm Bilson, who favors us with a Mozart concerto below.