Do you mean fearless in reference to themselves and their lives or do you mean that nothing scares them. Like the thought of loved ones or close friends dying because they failed in some way or another? I'd say Deathstroke is number 1. Don't know where I'd place the others though.
Both. I actually think both are one and the same (even though you'll probably disagree with me) but I'm glad you've asked this question...it will lead from it being asked again by another poster. Lets use both. Can you add this to the OP?
I wouldnt say it is quite the same. Not imo at least. For example I wouldn't call Spider-man fearless, he gets scared quite a lot. Does not stop him from overcoming the fear all the time.
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Azula: My mommy didn't love me so I'm going to burn down your village.
Batman, Captain America is to respected to be Feared, besides have you played Batman Arkham Asylum,City, and Origins, people SH!T there pants when they see Batman
Daredevil and early Green Lantern were supposed to be simply "without fear". They just didn't process it. I'm not sure how that held up with Daredevil. With Green Lanterns that got amended to having the ability (will) to overcome fear--presumably when they realized that a truly fearless person is more of a sociopath than a hero.
What about Deadpool? He seems screwed-up enough that I'm not sure if he processes fear.