I think Taylor in terms of longest lasting influence. But even though his book was written in the 1940s Americans did not seem to get bitten by the double bug until the late 1980s or so.

Perhaps, at the risk of being controversal, I'd also suggest Craig Boddington. He is one of the only "popular" gun writer who writes frequently on double rifles (I'm not forgetting Ross Seyfried and Sherman Bell here, but they are not as commonly known in the general hunting press). Think back to his book "Shots at Big Game," where he actually talks about double rifles in a general hunting rifle shooting book. What other major gunwriter writing for the general hunting public would do that in the late 1980s? Also his puplication of "Safari Rifles" was right in 1990 right when the double rifle craze just started so I imagine he had some influence there.

Just some thoughts...