Who's This? An old-school musketeer.
How you could have heard of him: Rebirth shows the Cavalier wearing the LotDK look, but no word as to whether he's Drake or the other guy. In any case, the character is killed on a Suicide Squad mission. Since he's a little silly, he of course appeared in several episodes of Batman: The Brave and the Bold (also, in DC Super Hero Girls).
Example story: Batman #22 (April-May 1944) "The Cavalier Rides Again" by Bill Finger, Jack Burnley and Charles Paris
Of course, the Dynamic Duo does escape and the note is an elaborate clue to the Cavalier's next crime. They don't solve it right away because Bruce Wayne ALSO has that dinner to go to. A "quirk of fate" seats the two men together, unawares!
I quite like the idea of a Batman rogue whose gimmick is collecting bougie stuff. There's the same variety as committing, say, crimes based on jokes, cats or birds, but it actually makes sense that a top-one-percenter would get his kicks assembling an illegal collection of the beautiful, rare or sophisticated items. It's too bad the Cavalier fell out of fashion. This story makes him out to be a criminal version of Bruce Wayne, and just as smart if not quit as capable. Well, it IS Batman's book after all.
Who's Next? A traveler inside earth.