Well, the character’s original name was “Kal-L”, which I guess was Siegel and Shuster’s reference to other sci-fi works of the time where people in futuristic societies had zippy names like “Jordan-6” or whatever. The minor alteration to “El” (and the family histories in which an ancestor of Superman’s takes the name “El”, meaning “star”) came much later on, and the Superman “S” symbol being of Kryptonian origin started with the 1978 film.
In one 1960 story where Superman gets tossed back in time to land on Krypton a few years before his birth and the planet’s destruction, he romances an actress named Lyla Lerrol.
Lots of “L.L’s,” but no Kryptonian “El-El” that I’ve ever seen, and I’ve been reading Superman comics pretty consistently for well over 50 years. It’s probably just as well that Mort Weisinger never thought of that, since it would have undoubtedly made a silly story.
I remember a Silver Age Superman story in which he received a box which could supposedly tell the future when you asked it a question. It always gave the same answer: “LL”. Those were always the correct initials, however. One person asked who would save Superman’s life that day, if he was in danger. “LL” was the answer again.
Big surprise: Superman was exposed to kryptonite. He figured that one of the many people he knew with those initials would save him, but none of them did. Then a kid spotted him and closed the lead box containing the kryptonite, saving his life. Superman asked his name, and the boy said, “Steven Snappin.” Huh? Then Superman figured it out…
Actually in early strips, Superman’s father was given as “Jor-L.” It was later reconned as being the father of the Earth-2 Superman.
As for “LL,” Lois Lane was there from the first appearance. “Luthor” was the next to appear – but he originally had no first name.
In the 50s “LL,” began to proliferate. “Lana Lang” came next, probably because she was seen as the Superboy version of Lois Lane. Lori Lemaris was probably the next – again, another love interest for Superman/Clark Kent. By that time, the writers uses the “LL” theme whenever they could get away with it.
When I was reading Superman (mid-‘60s), the letters page would include readers’ contributions of punny Superman family names, like Gav-El the judge, or Tow-El the locker room attendant.
That’s the reason given for calling the Incredible hulk’s alter-ego David Banner instead of Bruce in the live-action TV show (even though Bruce really is his middle name, Robert Bruce Banner in the comic books). Kenneth Johnson wanted the series to be taken more seriously, so he removed what he perceived as a staple of comic books, that is, major characters having alliterative names such as Bruce Banner, Peter Parker, and Reed Richards.