Final answer:
Gloria Steinem was the first woman art director of a mainstream magazine through her role in co-founding Ms. Magazine, which focused on women's rights and empowerment.
Step-by-step explanation:
The first woman art director of a mainstream magazine was Gloria Steinem when she co-founded Ms. Magazine with Dorothy Pittman-Hughes. Ms. Magazine broke away from traditional women's magazines by focusing on women's rights, empowerment, and social issues rather than homemaking and fashion. Steinem, a prominent advocate for women's rights, leveraged her journalistic experience to tackle serious issues and elevate the magazine as a platform for feminist discourse and a pioneer in presenting subjects such as domestic violence, sexual harassment, and body image concerns to a national audience.