Demogorgon

The Demogorgon is one of the most powerful demon lords and is often referred to as the “Prince of Demons.” He rules over the 88th layer of the Abyss, an endless, corrupted jungle realm full of monstrous creatures and demons.
He possesses a gigantic, scaly-furred body with two long tentacle arms and two demonic heads, each with its own consciousness. These heads are called Aameul and Hethradiah. They constantly fight each other for control over the body, making the Demogorgon both unpredictable and dangerous.
As a dangerous antagonist in the campaign book “Out of the Abyss,” he is one of the greatest threats to the world of mortals. He is a brutal being that spreads madness and chaos and instills fear in even other demon lords.
Many also know his name from the series Stranger Things, in which both Dungeons & Dragons and a monster named Demogorgon play a role.
Here you see the trailer for the first season of the series Stranger Things, in which a Demogorgon also plays a role:
Asmodeus

Asmodeus is the supreme lord of the Nine Hells and one of the most powerful beings in the world of Dungeons & Dragons. He is regarded as the god of tyranny and contracts and is considered the archenemy of all righteous gods. He rules the devils from his throne in Nessus and aims to gain control over all worlds and their beings.
When appearing to others, he often uses avatars to present himself. Outwardly, Asmodeus often appears as a charismatic red tiefling. His true form is so terrifying that few have ever seen it. He is equally intelligent and powerful and pulls the strings over all planes of existence through clever intrigues, contracts, and temptations.
Asmodeus, as the master of manipulation, is one of the most powerful antagonists for many campaigns, plunging heroes into ruin through contracts – or making them believe he is the only hope against even worse threats.
Orcus

Orcus is one of the most powerful demon lords in the lore of Dungeons & Dragons and is considered the lord of the undead. He rules the 333rd layer of the Abyss named Thanatos, a dark realm full of necropolises and undead.
Orcus is a gigantic, 4.5-meter tall demon with goat legs, bat wings, pointed horns, and a skull for a head. Unlike other demon lords, he is not only concerned with chaos or destruction – he wants to extinguish all life and engulf all existence with undead.
His favorite weapon is the famous Staff of Orcus, a powerful artifact that can kill any living being with a single touch. He can also poison any enemy with his tail. All this makes him a villain that players should not underestimate, and even gods and other demons are reluctant to confront him.
Page 3 continues with Acererak, Iymrith, and Xanathar.