Angus McQueen, whose Midwest advertising agency was a principal architect of the National Rifle Association’s modern image until the firm had a remarkable falling out with the gun group this year, died on Tuesday in Oklahoma City. He was 74.

Ackerman McQueen, the Oklahoma City advertising company that Mr. McQueen had long led, announced the death. He had had lung cancer.

Mr. McQueen’s death came amid a legal fight between the N.R.A. and Ackerman McQueen that would have not long ago been considered inconceivable.

The two organizations had been so close for nearly 40 years that some of the most recognized faces associated with the N.R.A., including its former spokeswoman Dana Loesch and its former president Oliver L. North, were actually on Ackerman’s payroll, not the N.R.A.’s.