Morten - opinions differ, but the consensus seems to be that Joseph Lang in about 1907(or slightly earlier) introduced the .470 Nitro Express cartridge.

Quotes from "Arms & Explosives" of May 1907 partly tells the story;

"...Two new Cordite rifles have been introduced with an excess size of calibre which would allow them to escape the prohibition under the Indian Arms Act of the .450 bore". Hollands had recently introduced their .500/465 bore, and A&E went on to say.."the new Lang rifle for which Kynochs have produced two weights of bullet, viz one of 500 grains and one of 365 grains". Unfortunately, the calibre was not stated specifically, but in the same notice, A&E described it as .."the 465, .475 or whatever the larger calibre happens to be". Slack journalism, even in those days!

Langs' involvement in .470 development is further supported by the fact that prior to May 1907, "The Field" was testing a .470 calibre Lang rifle.

Despite it's obscure history, the .470 cartridge was to become entrenched as a double rifle standard of the British Gun trade; the major proponent being John Rigby, who probably made more doubles in .470 than all other calibres put together.

As such, while Lang may have invented the .470; Rigby was the gunmaker that popularised it