"Bell Aircraft Corp is founded at Buffalo, by Lawrence D Bell, Foreman and later General Manager of the early Martin factory in Los Angeles and for many years Vice-President and General Manager of Consolidated Aircraft."
"Company activities during 1935," A Chronicle of the Aviation Industry in America, 1903 - 1947, privately published by Eaton Manufacturing Company, Cleveland, OH/
Bell's first plane, the YFM-1 Airacuda "convoy fighter" was not a success. Their next design, the P-39 Airacobra, on the other hand, was. The successor to the P-39, the P-63 Kingcobra, appeared late enough in the war that it was not a significant factor in the fighting. Both P-39 and P-63 are covered in the P-39 section, as is the experimental XFL-1 Airabonita.
Bell developed other fighter designs during the war, most notably America's first jet, the P-59 Airacomet. The XP-77 was an all-wood design intended to avoid a possible shortage of aluminum; since the shortage never materialized, the all-wood designs were mooted.
Bell also produced 668 license-built B-29 Superfortress heavy bombers at a plane in Marietta, GA 357 B-29-BA and 311 B-29B-BA (BA for Bell Atlanta). The Wikipedia entry for Bell Aircraft Corp states that Bell also built B-24s at this site, but none of my other sources mentions such production.
The to-be-famous Bell helicopters had their initial development during the war, but did not become active until after the end of WWII.