Matael

The image above is Matael's own perception of himself. But the character URIEL may as view him as such too.
Otherwise, he appears as a normal looking guy to everybody else. With the exception of when Samael's soul surfacing, in which case he does also look like that. 

Matael, while still somewhat "human", is one of the few characters that lives outside the set "Loops". This is because his body/vessel holds two souls: Matael and Samael.

the soul Matael is a resident of the world, it is bound to it and would normally always be kept in the loop. However, Samael is an angel created by God (the character) and therefor an outsider to the world.
Normally angels are also kept inside of the loops, but because of the fact Samael (a pure pale soul) is bound to Matael (a gray human soul ), the body is rendered "impure" and therefor rejected by the world and it's looping system.

Samael was bound to Matael in an experiment conducted by URIEL in order to escape her divine punishment, but all it did was simply share her punishment with someone else instead.
Unlike URIEL, because of his partial human nature Matael's memory resets, making his sentence lighter. Although, this does not stop the partial degradation of his soul. It does however prevent the degeneration of Samael, which would've been present in other angels.

In terms of personality, Matael is a very reserved but kind individual. Though he may seem introverted, that is less because of shyness but more an inability to express himself properly. Some of his actions may look completely irrational but those who know him do understand there is some level of thought behind them and they usually have good intent.
Though, Matael is also incredibly dependent on URIEL, who through the majority of the story, he houses inside of his mind. Without URIEL, Matael cannot see himself able to function and constantly seeks her approval.
This allows URIEL to easilly make him do certain actions, which almost always end up in her eventual resuscitation.