To first answer this question, one must know what the traditional concepts of both the hero and the villain are.
The traditional hero is one who looks out for the community which they serve (sometimes can be global), appear larger than life, has great strength (both physical and mental), and is looking to simply save the world.
The traditional villain is set up against the hero. The villain does not care about anyone but themselves, must bring down their nemesis (at all costs), and fails to possess typical morals.
In this sense, neither Blanche nor Stanley (from Tennessee Williams' play A Streetcar Named Desire) can be considered heroes. Both are not trying to better the world. Both are not larger than life. Both do not have great strength. (In reality, both are very weak characters.)
That being said, Stanley does fit the villain stereotype very well. He, based upon his bitter hatred for Blanche, needs to bring her down. From the very beginning, Stanley does not like Blanche. He sees her as a thorn in his side (fights with Stella, concerns about her telling the truth). Stanley also rapes Blanche. No hero would ever be able to do this.
Blanche could also be seen as a villain. Blanche despises Stanley. She tries to talk Stella into leaving him. Therefore, she tries to take down her nemesis (Stanley). Blanche does not possess good morals. If she did, she would not have prostituted herself or tried to hide who she really was.
In the end, neither Blanche nor Stanley can be considered a traditional hero, but both could be considered villains.