Harry Turtledove

Harry Turtledove is that rarest of things: an AH author with mainstream name recognition.

Probably more read than any other AH author on the market. An inevitable side effect of this is that he's also one of the most criticized AH authors on the market, simply because more people are able to participate.

Author of the TL-191 series, The Guns of the South, and a great many others.