Lucifer,morning star, The Lord of Evil and Decieve, and lies.
Lucifer
Yes he is. Sesshomaru is a very powerful demon. he even surpassed his father who is said to be one of the most powerful demon in the Inuyasha world. and it is said that when it comes to raw power no one can beat Sesshomaru.
there is no such thing as powerful anything except what god gave them
There's no definite answer, but it's probably Lilith. Lilith was the first demon created by Lucifer and is considered the mother of all other demons.
The most powerful demon is the one who can cause suffering to both humans and ghosts. He/she takes many forms and names through out different religions and culture.
The name "Lord of the Flies" is a literal translation of the name of the biblical name Beelzebub, a powerful demon in hell sometimes thought to be the devil himself.
I don't know about Demon Child. But the name Raksha means Demon.
Beelzebub is often portrayed as a powerful demon in religious texts.
He controls a Jinchuuriki, the one tailed demon.
Summoning a demon requires correct and complete knowledge of the "true" name of the demon you intend to summon.
Demon Dan's birth name is Daniel Blackner.
One demon is often refered to as 'Satan'.