Age: Unknown
Gender: Male
Eye Color: Dark
Brown
Hair Color:
Dark Brown
Social Status: Prince of Rei kai
Strength Level:
Unknown
Seiyuu: Tanaka Mayumi

The Prince of Rei kai:
Koenma fears his father, Enma Daioh and dreads his anger. His servant
and friend, Jorju Saotome, an oni, shares the same feeling towards the
god of Rei kai.
He often appears as his
toddler form (see picture above). His appearance made him look less
dignified (in Yusuke and Kuwabara's opinion), therefore at the sight of
him, they tend to make rude remarks rather than show any sign of
respect. Botan, who is a Rei kai ferry girl, often ends up hitting the
two and forcing them to show respect their respect for him.
Despite the two's
disrespectful attitude towards Koenma, they became friends. When Yusuke
and Kuwabara received the invitation to compete at the Ankoku Bujutsukai,
Koenma agreed to be the head of their team (the Urameshi Team), and they
began to see him more, since he, Botan and Jorju came to watched the
tournament live.
When Yusuke found out that
he has a Class S youkai blood on his veins, Enma ordered the Class A
army of Rei kai to eliminate him. Koenma, not believing that Yusuke will
go evil when he died, disobeyed his father and helped Yusuke survive.
This meant a lot, because he never disobeys his father.
Later in the series, after the tournament at Makai ended, he allowed
Yusuke to live a normal life by removing him as his Rei kai tantei. He
claimed that they will not see him for a long time (about 3 years),
probably because, during those three years, peace will reign between
Makai and Ningenkai.

Observations:
I have never seen Koenma get into fights, and I've never seen him hit a
person that's not Jorju. He doesn't have any fighting style or any of
the sort. He loves to eat, though, like his faithful assistant (Jorju),
and is willing to do anything, even cheat, just to get food.
Koenma is often followed by two people: Jorju and Botan. Jorju must have
claimed the responsibility of taking care of his Prince and Botan awaits
for his next command. During the Makai Tournament, all three went in
disguise so they could come and watch the fight live. Actually, Jorju
was supposed to be left behind, but he followed the two. They kept their
disguises to prevent from being eaten alive. Koenma is really a coward,
but when it comes to his friends, he's willing to stand up for them,
even if it means angering his father.

The Pacifier:
The pacifier stuck in his mouth is used as the storage place of his
powers. This powers brought the dead back to life, namely Amanuma, the
Gamemaster (from the Sensui Saga). Aside from bringing back the dead
alive, he can also use the power to trap a person/youki with a shield.
You can learn more about him and his powers in the Sensui Saga.