Spiderman, I think the first character that was based on who the audience were so they could relate to him easily.
Or professor Xavier, a leader who was crippled?
Or Storm, first major character who was a black woman and could stand up for herself.
From that I'll say whichever female character who was the first to make the change from 'girls are the prizes who are there to be rescued' to girls being able to stand tall with men characters, in their own way. I don't know which character did this transition though.