What is it that makes a person fearless?

Ignorance

Courage because when a person knows he has overcome he's fear or any fears he knows that he is invincible

Honor can over come fear as a person is doing what he believes

Integrity and self-sufficiency a person who believes he can overcome anything is fearless.

Adrenalin in a situation can make a person do things he might have thought he would never do, you can only run on adrenalin if you are in a situation in which you are threatened

I give a lot of credence to the answer by Sophist. That's my experience. The times I have been credited with bravery, or with boldness (in the case of work stuff) I was only acting because there was no one else to act. It was down to me.

The more general answer, which I think can incorporate both your answer and Sophist's answer, is that a "fearless" person is using a simple risk/reward assessment.

I propose that a person instantly (and perhaps even subconsciously) weighs the consequences--physical, mental, and spiritual-- of giving in to fear or facing fear. It's important to add "mental and spiritual", because it explains why people put themselves in the way of physical harm. The physical harm is preferable to the mental knowledge that you did not act.

One faces fear when giving in has worse consequences.

It depends on the person. It could be extreme courage or extreme ignorance. I'd say it's more likely to be the latter. No one is truly fearless in a dangerous situation if he knows the risks. Some people just control their fear better than others.

Fear is an emotional response to threats and danger. It is a basic survival mechanism occurring in response to a specific stimulus, such as pain or the threat of pain. Psychologists John B. Watson, Robert Plutchik, and Paul Ekman have suggested that fear is one of a small set of basic or innate emotions. This set also includes such emotions as joy, sadness, and anger. Fear should be distinguished from the related emotional state of anxiety, which typically occurs without any external threat. Additionally, fear is related to the specific behaviors of escape and avoidance, whereas anxiety is the result of threats which are perceived to be uncontrollable or unavoidable. Worth noting is that fear always relates to future events, such as worsening of a situation, or continuation of a situation that is unacceptable.

Nerves of steel, or the brains of a rock. In the former case, it's realizing there's nothing to fear but fear itself, understanding that anything in life can be dangerous, but the desire to live life is stronger than the threat of punishment. In the latter, it's just being too stupid to realize that no one is invincible, and is unable to discern between a calculated risk and a moron's move.

I don't think anyone is fearless, it is choosing to overlook or ignore the fear. Or maybe you have not come across the thing that makes you fearful yet

Empowering belief in a purpose or exceedingly strong desire for the accomplishment of an end that overwhelms the restraints of common reason.

Someone who has mentally mustered the perception that "fear" is a little crying baby within his mind. Fear is contageous within the mind. If we are afraid of one thing, it can transmit to other experiences. Likewise, when we face fear in numerous circumstances, it becomes much easier to face fear in specific areas that we trifle with.

I think your mistaken/confused. There is no such thing as a fearless person, there is something called courage, but being courageous is not having no fear, it is being able to face your fears.

There is no such thing as fearless.

Peace out.