When I first heard about Rosa Parks, many years ago, I didn't realize that she had been a civil rights activist before her famous refusal to vacate her seat on the bus, and that she was deliberately setting up a test case. I assumed, rather, that she had not been particularly political, and that the idea of standing up for herself was a spontaneous response to a last straw. I would guess that many in the civil rights movement implicitly encouraged such assumptions, although I'm not aware that Ms. Parks herself tried to obscure the truth. I don't think that her activist history in any way diminishes what she did -- but it makes for a different story than the mouse-that-roared version. Perhaps a less thrilling story, to some -- but I'm for knowing what really happened, when possible.
A September 19, 2005 Village Voice article stated that Cindy Sheehan "may be the Rosa Parks of the anti-war movement." That may be true in ways the Voice didn't mean. While I don't think she was a particularly influential activist before her son's death, she was a highly political animal, anti-Bush and generally left-wing. And Sheehan herself has tried to use the popular misconception to her advantage.