In "What Was Missing," the Door Lord steals Finn's precious wad of Princess Bubblegum's hair, Jake's baby blanket, BMO's game controller, a little kid's toy train, and Princess Bubblegum's rock t-shirt given to her by Marceline. To recover their possessions, Finn, Jake, PB and Marceline spend the majority of the episode trying to figure out how to open the large door that the Door Lord is hiding behind. When the group finally succeed, they corner the Door Lord, who is eating a sandwich, in a room paneled with drawers of objects. Despite understanding the Door Lord's explanation for stealing their stuff, they beat him up and leave him tied up in his lair.
The Door Lord has the ability to instantly create doors to take him places, as seen in "What Was Missing." He appears through a door he created, and later leaves through another door. When he creates a door, he does so by throwing a small key at whatever place he wants the door to be appear. Each door appears on the spot, unfolding quickly, and the doors can appear floating in the air and/or tilted, and still function. The Door Lord also seems to have the ability to open any door that is already made. He can also jump very high to reach his doors, which Jake acknowledges by saying, "That guy must do crazy squats!"
The Door Lord looks very similar to Key-per and Booko, having the same skin color, big cheeks and blue hat with a strap, but is much taller and has more muscle mass and his chest is sunken. He has multi-jointed appendages, allowing him to move and bend in abnormal ways. His legs bend backward then forward, like a deer or horse's hind legs. He has four joints in each of his arms, not including his fingers or shoulders. He has large pecs, and seems to have visible ribs.
The Door Lord also wears a small door attached to his hat, which is similar to the way Key-per wears a key on his head. He wears no clothes. He does wear a bright blue cylindrical knapsack and string of keys across his chest.
Door Lords maintain a vow of silence and do not speak. However, Door Lord mumbles in response whenever he is addressed, but his mouth never opens and his voice is muffled beyond comprehension. Sometimes what he is saying can be translated, as when he was asked who he was, and seemed to hum, "I'm a Door Lord!" Marceline and the others in the group were somehow able to understand what he was trying to explain near the episode's end, though they may have been guessing correctly instead of directly translating his muffled words.
- The Door Lords appear to be of a similar species to the Key-per and Booko, but they are very different in many ways.
- Key-per has the power to open a door with his big key hat, while the Door Lord possess the ability to create doors to anywhere.
- Key-pers are small in appearance, whereas Door Lords are giants who tower over the rest of the characters easily.
- While Key-pers are known to be very fast talkers, the Door Lords sacrificed their ability to speak in exchange for the ability to travel through time and space.
- The Door Lord appears in the Cartoon Network game "Finn and Jake's Epic Quest." Successfully hitting him will yield a random page from the Enchiridion.
- There is a slight resemblance between the Door Lord and the Love Giant from the Japanese video game "Doshin the Giant."