" A simple reason really. I'M EVIL!" --Negative Numbuh 4
Negative Numbuh 4 is the Supreme Leader of the Destructively Nefarious Kids, an evil version of the Kids Next Door Organization that exists in a parallel Negative Universe, and the tyrannical ruler of that universe before his defeat.
When the main characters entered the Negative Universe through a portal in Wallabee's new backyard pool and Negative 4 discovered the existence of a positive universe, he sent Eizzil to capture her counterpart Lizzie in a bid to take over the positive universe.
After successfully capturing the members of Sector V and replacing them in their universe with his servants, Eeballaw revealed himself to his captives, but they mocked him on his goatee. In response, Eeballaw declares that positive Sector V and Lizzie will fight each other in the arena and all but the winner will be sent to the broccoli mines while the winner will become his "bestest bodyguard."
Negative Numbuh 86 made a weak protest, only to be harshy rebuffed by Negative 4. Nigel mocked Negative Numbuh 4 and declared that they will never fight each other and rule alongside someone who rules by using fear, so Negative Numbuh 4 orders his guards to take the prisoners to the broccoli mines.
With that settled, Eeballaw returned to the pool, waiting impatiently for his minions to secure the positive universe's pool and begin his invasion. Before he could do so, he found his minions resurfacing and greatly injured. Shortly after, Numbuh 4 jumps into the pool and enters the Negaverse, facing his negative counterpart on the diving board, with the Negative version bragging that his guards and superior intellect gave him the advantage.
However, Wallabee recognized that his foe was everything he was not; therefore, he was also an utter coward. Although Eeballaw tried to deny the accusation, Eeballaw's challenge caused him to order his guards to fire. Unfortunately for Eeballaw, this display of cowardice - coupled with a regretful Ynnaf's impassioned speech to her teammates - led to the DNK turning against their leader and realizing the error of their ways.
After a short rant about his team's betrayal, Eeballaw leaped into the portal to the positive universe, only to be kicked back to the negative universe by Eizzil. He was then apprehended by his former minions, who sent him to his own broccoli mines as punishment for his crimes against the Negative Universe.
Eeballaw appears identical to his positive counterpart, apart from a black goatee on his face. He claims it makes him look "eviler", but it's the source of much ridicule from both allies and enemies alike.
As with all inhabitants of the Negaverse, his personality is mostly the inverse of his positive counterpart. Although both Numbuh 4s possess a short temper and a boisterous personality, Eeballaw is much more intelligent and calculating than his heroic counterpart, able to coordinate the DNK through a combination of good strategy and simple intimidation.
However, he is also extremely cowardly if confronted directly, as opposed to Wallabee's fierce courage and hot-headedness. Consequently, he's almost totally reliant on his subordinates for protection; which, given their fear-based loyalty, is entirely dependent on his ability to keep up a threatening image as leader. Eeballaw also appears to act somewhat childish, as he uses words such as "toys" to describe his weapons.
Eeballaw shows no apparent attraction towards Ikuk, nor she towards him, displaying the opposite of their positive selves.
- Negative Numbuh 4 has a black goatee, referencing the evil version of Spock from the famous Star Trek episode "Mirror, Mirror", which the entire episode is a parody of.
- His real name might be Eeballaw "Yllaw" Seltaeb.
- Since Wallabee hates Rainbow Monkeys, it may be possible Eeballaw secretly loves them, but is too afraid to admit it to due to keeping up with his fearmongering attitude and his cowardice.