Originally Posted by
Digifiend
I think the answer might be Kitty Pryde and the X-Men in Days of Future Past. Future Kitty was sent into her younger self's body. Remember, in the silver age, Marvel had one singular universe, but DC had Earth-One and Earth-Two... which is why it only took a few years before Barry met Jay (it would've been considerably longer before anyone met a doppelganger - Barry certainly didn't meet a doppelganger of himself that early). Did Marvel even do multiverse stuff before the 1980s, except for What If which I'm pretty sure never involved anyone meeting a counterpart of themselves?