"Before I die, I will bequeath to one of you villains my vast empire and extensive power which I have spent 1,000 years building." — Queen Entozoa[source]
Queen Entozoa was the villainous queen shown in "The Fancy Party". She was dying so she hosted a party and said that she would bequeath her power to the toughest of villains. In the end of the episode, it is revealed that her "power" and true identity was a slug-like demon that was possessing her body for 1,000 years and needed to switch bodies so it could possess a new body for another 1,000 years, however it accidentally became a sandwich for 1,000 years due to Wander's meddling.
Not much is known about Queen Entozoa's true personality as she was merely a vessel for the creature that was possessing her. What she was like 1,000 years ago before being possessed is unknown, however since she was chosen as the creature's host, it can be assumed that she was an evil villain. While Sourdough was possessing her, she often acted like a feeble yet ruthless old woman who admired power and notoriety above all else.
She was good friends with Wander because as she states, he's the "number one most wanted fugitive in the galaxy". She, of course, does not realize Wander is not a villain, nor that he's only wanted because of Lord Hater's influence. However, after Wander caused her to be trapped in a Sandwich for the next thousand years, Sandwich vowed revenge.
She at first didn't like Lord Hater and was constantly annoyed by his attempts to win her over, such as singing her a sappy mushy love song, but after seeing his ruthless display of power, she seemingly grew "fond" of him (but in actuality she became fond of his power). She was originally going to give Wander her power but instead, Lord Hater proved to be more gruesome, so she gave him her power. It turns out that her "power" was a slug-like demon which had taken over her body 1000 years ago and was the true puppet master of the queen and it planned to take over Hater as its next host. The slug then entered Hater's mouth, choking him, so Wander did the Heimlich to save him, causing the slug demon to be spat out and land into a sandwich, causing it to become Sourdough the Evil Sandwich.
"The Fancy Party" (First appearance)
She was the first known common enemy to both Wander and Lord Hater.
She was the first character to actually die.
Also the first character to show a death happen to her.