Some superheroes get rad secret identities. By day Superman is Clark Kent, an investigative reporter for the Daily Planet whose work places him in situations where the Man Of Steel is needed. When he's not skulking around Gotham's rooftops as Batman billionaire socialite Bruce Wayne attempts to affect change in his city by spending money on public services and new technology. Oliver Queen spends half his time as Green Arrow, and the other half...pretty much in the same way that Bruce Wayne does. Barbara Gordon's writers, meanwhile, decided Batgirl could do with a day job as well. And what they decided upon was...librarian. Not just any librarian, though! No sir. Barbara Gordon had a doctorate in library science, which allowed her to take the head position at Gotham City public library, One of the largest public libraries in the DC Comics version of reality. It sounds a bit un-cool, and certain creative teams did reduce her to the stereotypical dowdy librarian types, but it actually makes a lot of sense for the character. An autodidact with photographic memory, it was a perfect place for her to hone her various skills and start along the road to the hyper-intelligent cataloguer of bad guys, Oracle.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/