(or "'Spin-Off': Is There Any Word More Thrilling To The Human Soul?")
Over the years, the Legion of Super-Heroes has become one of DC's mainstay titles, an icon every bit as important to the fictional universe as the Flash or the Justice Society. It's gotten its own cartoon, it's maintained a fanbase through three complete continuity reboots, and it's kind of hard to remember now that it started off as a one-off appearance in the Superboy section of 'Adventure Comics'.
Yes, the Legion of Super-Heroes is a spin-off, and arguably one of the most successful spin-offs in history. (Did 'Frasier' get his own cartoon series? I don't think so.) But what is it about the Legion of Super-Heroes that made it such a successful spin-off? What elements made it succeed where so many other spin-offs wither and die?
For starters, it had an instantly accessible central premise. "In the future, teenagers will have super-powers and they'll hang out together in a clubhouse, fighting crime." It's a perfect idea. Most of the readers at the time were kids themselves, and they'd probably formed a club or two of their own at some point, and many of them probably even had a clubhouse. The "future" and "super-powers" aspect just plugged right into the love of science-fiction that was infusing comics with new life in the Silver Age. (Which means that logically, they should be doing a manga reboot of the series now...but I digress.)
Even the names are instantly accessible; sure, in the 80s and 90s, when comics became more 'serious', the naming conventions of the Legion took a drubbing, and many of the Legionnaires decided to start going by their real names, but as hokey as they sometimes sound, when you read about 'Colossal Boy', 'Lightning Lad', and 'Braniac 5', you've got a pretty clear idea right off the bat of who these people are and what they can do, which is important for a series with a large cast that wants to attract new readers. Legion comics in the 90s advertised with a poster that was nothing more than a giant flowchart of the various characters and their relationships to each other, not understanding that advertising, "Hey, we're complicated, confusing, and have a large cast!" might not be the best way to go in attracting fans. Having an easy "hook" to hang on each character might have made for simplistic storytelling at first, but it did make them memorable. (And memorable characters have a better chance of succeeding.)
Setting the comic in the future helped a lot as well; I've talked in the past about worldbuilding, and by placing the comic in the 30th century, the writers of LoSH have an almost unlimited opportunity to do just that. They can explore the future of Earth, hop to strange alien planets, play with the conceit of time travel, and in general make use of science-fiction ideas too outrageous for comics set in the present day.
Most importantly, though, they made good use of their "parent" title. Superboy was a member of the Legion, as was Supergirl (the Super-Pets had their own 'Legion of Super-Pets', of course.) Over time, as the "Superboy" concept grew less popular, the Legion gradually began to de-emphasize him on the cover, but he was always an integral part of the Legion--and not just within the pages of the comic itself. Superboy helped sustain interest in the title until a fanbase could cohere around the new characters, and appearances by his enemies (such as the infamous Lex Luthor) helped the writers think of stories while the Legion's own rogues gallery accumulated.
Ultimately, this was the only real mistake DC made with the Legion. By removing Superboy from continuity, they left a hole at the heart of the Legion, one which reboot after reboot has never quite managed to fill. Worse, by rebooting again and again, they've added a significant new element to the Legion's storytelling engine--notably, that it gets blown up every five to ten years when a new writer comes along who doesn't like the direction the book has gone. (Reintroducing the old versions of the Legion only makes things even more confusing.) One can only hope that DC will stick with the current Legion for at least a while...as mentioned at the beginning, the Legion of Super-Heroes has maintained an impressive fanbase, but their patience isn't indefinite.