Gail Simone, writer of beloved series like Clean Room, Birds of Prey, and Batgirl, has revealed that while writing the adventures of Barbara Gordon (aka Oracle), she secretly intended the Gotham hero to be working with Marvel's Iron Man. It's been a long time since Marvel and DC were open to comic crossovers in which their heroes helped each other out - though there was a time when the Amalgam Comics line literally combined their heroes into one - so Simone never made this idea explicit, but there is a character in a DC comic who the writer considers to secretly be Tony Stark.
Simone's popular Birds of Prey run saw many of DC's street-level heroines working under the leadership of Oracle - the name Barbara Gordon took on after she was shot by Joker and (ultimately temporarily) lost the ability to leap across Gotham's rooftops. Simone also wrote for Batgirl during DC's New 52 reboot, and recently answered a fan question about how Barbara learned the skills she needed to make the transition from boots-on-the-ground hero to the all-seeing, all-knowing tech genius who rivals Batman as Gotham's most important hero.
Asked by a fan on Twitter how Batgirl learned to hack, Gail Simone responded that Barbara has a natural affinity for the subject - and as the fan observes, she clearly studied her craft - but that she also consults with a group of peers known as the Stable, who it's implied helped her develop her hacker skill set. Simone goes on to say that in her personal headcanon (an idea about a story not spelled out in the text, but held by individual readers as true), the Stable were communicating with Barbara from different universes, and one of them was Tony Stark.
First introduced in Birds of Prey #63 - from Simone, Ed Benes, Cliff Richards, and Alex Lei - the Stable are a group of high-level hackers. "If you want to read the president's email before his aides do," Barbara notes, "then you want these guys." Known only by the colors of their individual symbols - a red man, a pink yin-yang symbol, a white angel, a blue X, and a yellow biohazard symbol (plus Oracle's green icon) - the hackers consult on difficult cases without ever exposing their identities or even connecting systems. While fans believe Blue is Ted Kord, aka the Blue Beetle, and White is revealed to be someone named Jessica, that still leaves several candidates to be the incognito Iron Man.
Of course, Barbara Gordon is a genius in her own right, so it's not like she was ever Tony Stark's sidekick, but it's easy to see how being able to bend the ear of a group of tech geniuses from other universes would speed up Batgirl's evolution into Oracle. It's unlikely Gail Simone will ever get to make this headcanon official in the current comics landscape, but the next time Batgirl fans read Birds of Prey, they can spend a moment figuring out which member of the inter-dimensional tech collective is Iron Man, and maybe add some headcanon details of their own (for example, that Tony chose a biohazard symbol when he was mired in self-loathing around the events of 'Demon in a Bottle.')
Source: Gail Simone