Beelzebub IV (ベルゼバブ4世, Beruzebabu Yonsei) is an infant demon lord, and the son of the Great Demon Lord.
Beelzebub is a baby with an abnormally wide build and green hair. Beel is almost always shown with his binky, save when he is being fed. Usually, he is seen nude (even in public), causing ordinary people to talk about him and his "parent" Tatsumi Oga. Partially due to Hilda's misdirection, the rest of the Oga's family believes that Beelzebub is Tatsumi's biological son, using their similar eyes (usually frozen in either a blank stare or an intimidating glare)
Baby Beel is very easily impressed, especially by strong people since he himself is still weak and loses to other babies as well as to cats. On the other hand he is not the smartest one out there and tries to force his way through the most simple problems. It is also shown that he is afraid of insects. He often displays a fondness for things that might frighten "normal" babies, such as violence, exposed muscle tissue (on an anatomy model), heavy metal music, and demonic toys.
Baby Beel used to be a crybaby who used to cry and shock Oga all the time, but as the time goes on he gradually becomes braver to a point where he is now rarely seen crying at all. This is due to Oga's continuous teachings about what it is to be a man and a Demon Lord.
Despite having his own sense of pride and power, Baby Beel can be very shy around girls who are around his age, most notably Futaba and Chiyo Aiba. He tends to listen and follow the two out of apparent fear, perhaps intimidation of them. When around either of the two, he has even demonstrated embarrassment at the fact that he's always nude around them, something that generally doesn't bother him in the slightest.
Hilda has been chosen to act as the mother of Beelzebub, and raise him in the human world along with Oga. Beelzebub is close with his wet nurse, Hilda, as shown when she was stabbed by Hecadoth, he cried and even though Oga told him not to cry because Hilda is still watching them, he was still on the verge of crying. He also refused to run away when Hilda told them to run away. Also at the first series, Hilda asked if she should come with Oga to school, Oga refused. That caused Beel to cry and electrify Oga for not letting Hilda come with them.
When Baby Be'el is caused to cry for one of various reasons, for example Oga being in danger, it fries everything in a certain range depending on how loud he cries. Generally the energy used is higher than that of a 12.000 Volt stun baton Himekawa of the Touhoushinki uses against Oga in chapter 9. Initially, if Beelzebub was more than 15 meters away from Oga, the electric shock would reach a fatal level (for Oga). Due to their new-found trust, this distance has increased, but only by 8 centimeters. Recently, Be'el has shown the ability to control his lightning and shoot it with enough power to defeat an ordinary demon.
While training with Saotome Zenjuro, a radio was used that made a "shadow" of Be'el. This shadow supposedly embodies the potential of its subject, and, as it was able to easily strike Oga into a boulder and crush that boulder, Be'el is hinted to have a large amount of fighting potential.
Later, when Be'el and Oga switch bodies, Oga is seen defeating numerous delinquent's using Be'el's body, implying that Be'el already has great fighting powers but doesn't know how to control his strength.
Super Milk Time
It is revealed by Oga that he is not the only one getting stronger and that Be'el also receives a large power boost when they use Super Milk Time and they also fused after using the "Super Milk Time". At 30 CC, he was able to block the axe of Basilisk, one of the Pillar Heads, and at 80 CC, he was able to shatter the axe. Super Milk Time is a time limited technique.
Super Croquette Time
In the anime, Oga can use Baby Beels power while Baby Beel eat Croquette than drinking milk. In reverse, Oga drinks Baby Beels favorite Milk while Baby Beel eat Croquette. In this form, Oga synchro with Baby Beel and Oga took control. He can beat Jabberwock's dragon Sodom without even failing. Oga can use a giant Zebul Emblem to destroy half of Akumano Acedemy building.
- In Animax broadcasts, Baby Beel wears diapers over his genitals.
- Baby Beel resembles Roronoa Zoro from the anime and manga One Piece.