I came across the phrase "La mamá de Tarzán" when reading Los años con Laura Díaz by top Mexican author Carlos Fuentes.
The part of the book was set in the early part of the 20th century if I recall correctly and immediately made me think of English phrases like "the bees knees" and "the cat's pyjamas".
But was it used right across the Spanish speaking world or just in Mexico? Was it just in fashion for a few years and then disappeared or do people still say it today? How widespread was it, or is it?
Well, I hunted around and here it is in its context in the book:
―Yeah, I'm the cat's pijamas ―repitió Dantón que ella de una comedia de cine americano.
―Oigan, muchachos éste se las sabe todas. He's the bee's knees! ¡Es la mamá de Tarzán!
―Cómo no, Yo Colón.
As you can see it's complicated by being in a mixed Spanish/English context with wordplay and including both "bees knees" and "cat's pajamas" so it could be equivalent to those, but it could also be that they are using all three phrases to refer to somebody who think's they are the best of the best. Which would give it two meanings maybe?