The irrepressible "CathyC" uncharacteristically strained credulity whilst retorting to Bryan Styble:
No one knows who the @$#% Zeppo is.
But first, first things first: as I recall, she used her showbiz married name Barbara Marx (even if she didn't legally retain it) for a year or two after she hitched Sinatra, soon enough transitioning to Barbara Sinatra.
Second thing second: No one knows who Zeppo was?!? Never MIND that his unique-single-given-name stage name is rare enough to be hugely memorable by ITSELF--Ringo, Sting, Cher, Slash, Oprah, Bono*--but he ALSO had four parallel showbiz names to reinforce Zeppo in the public's mind: Gummo, Chico, Harpo and Groucho, the last two of which remain to this day downright HOUSEHOLD names across America.
So no, Cathy, all KINDS of (English-speaking) Americans know who precisely who Zeppo was, even without his Marx!
What is BIZARRE is how Wikipedia's 2017 Notable Deaths roster is at this hour--3am ET--describing the late Barbara Sinatra as "American fashion model (Richard Blackwell), showgirl and philanthropist (Eisenhower Medical Center)", mentioning neither how she acquired her final surname, nor employing Blackwell's distinctive stage name!
* The Edge wouldn't apply here, of course, because that stage name always PROPERLY includes its definite article, even though nowadays Bono himself often drops it in conversation. That's as opposed to little ol' Yours Truly: during two brief Los Angeles chats with The Edge during the 1980s--the first of which was a late-night** affair which also just happened to feature interaction with that mercurial Nobel laureate with the funny nose, funnier hair and funniest voice whose name I so often forget--I realized that it might be an easy mistake to make (considering how clumsy it can sound to use it), so I DEFINITELY made it a definite point to use his definite article!
** Monday, April 20, 1987 into Tuesday morn, in several locales including poolside at The Sunset Marquis, on the east side of Alta Loma down that steep hill from The Strip.