Twins

I only bought a handful of books at Sasquan. One of them was Kate Wilhelm's classic Where Late the Sweet Birds Sang, which I had never read. I may post at least a mini-review of the book later, but thinking about it has raised a question in my mind.

Can anyone name any historical examples of twins who were notable for something other than being twins? One or both, identical or otherwise (though I'd prefer identical)? (Of course, there are plenty of legendary and fictional examples, from Pollux and Castor to Miles and Mark Vorkosigan, but I'm looking for the real thing here.)