Neptr

Neptr (or N.E.P.T.R., an abbreviation for Never Ending Pie Throwing Robot) is a pie-throwing robot Finn created solely to prank Jake who first appears in "What is Life?" He usually calls Finn "creator."

He came to life when Finn became frustrated that his shoddily-assembled "robot" wasn't working and threw the creation out into the rain where he was hit with a lightning bolt. This brings Neptr as we know him to life, though he isn't fully functional. Finn took him to Ice King's palace to use the villain's lightning bolts to fully charge him. When he was hit with Ice King's lightning bolt during the resulting battle, part of Neptr's personality was changed to a desire to collect princesses causing him to become slightly evil, but he also becomes powered up to full power. Neptr admires Finn's pranks and has decided to keep Finn as his companion, and has also decided to prank Ice King hardcore. However, he is shown to have some compassion, as he says goodbye to the (unconscious) Ice King before leaving with Finn, causing Ice King to shed a tear. After this, he and Finn throw never-ending pies at Jake.

Neptr returns in "Hot to the Touch," where it is revealed that he was hiding for 15 months, 4 days, and 9 hours in a game of Hide and Seek that was accidentally forgotten by Finn and Jake. He assists the two by constructing (crudely made) heat-retardant suits, while singing the "Working For The Master" rap, in order to get close to the Flame Princess.

Neptr once again returns in "BMO Noire," where he awoke BMO while it was unconscious. Neptr proposed that BMO and he should hang out more since they are both robots, but BMO rejects his offer saying, "I am not like you."

He later returns in "Mystery Dungeon", captured by the Ice King along with Lemongrab, Tree Trunks and Shelby. However, it was later revealed that Ice King meant to grab BMO and not Neptr. The Ice King seems to have forgotten about Neptr.

Appearance
Neptr is made from pieces of junk stuck together with tape. His components are an electric oven, a soup can, a circuit-board, wires, a tuning-fork and small tank treads possibly from a toy. Finn drew a face on the soup can, intending it to function as his face, but the knobs on Neptr's side became his face when he was brought to life.

Quotes
See Neptr/Quotes 

Finn
Neptr and Finn have a very good friendship. He helped Finn defeat the Ice King by pranking him in the decision to live with in the episode "What is Life?." In the end he chose to live with Finn to prank people like Jake. Even though mentioned in the episode, Hot to the Touch, that Finn and Jake left Neptr hiding in their shed after a game of Hide and Seek over about fourteen months, three days, and four hours he still moved on to help Finn and Jake create a battlesuit to save the Goblin Kingdom from Flame Princess. Neptr also sings the song Working for the Master saying in the song "I live to please you father" saying he thinks Finn as a father. After Finn cries over not finding a girl, Neptr says "I still love you" saying Neptr cares about Finn.

Jake
To Jake Neptr is a friend at times. In the episode "What is Life?," Neptr was sort of an enemy to Jake after he pied him to help Finn prank him. Though mentioned in the episode Hot to the Touch, Jake played Hide and Seek with Finn and him, indicating that they are friends. He also helps him and Finn create battlesuits to save the Goblin Kingdom.

BMO
In the episode "BMO Noire," Neptr awakens BMO and tells it that the only people down there was both of them and Ronnie. Neptr also offers BMO pie but BMO wanted to go find the sock. Neptr also says they should hang out sometime since they're both robots, but BMO replies "I'm not like you."

Ice King
NEPTR first interacted with Ice King in "What is Life?" when Finn wanted to fully function NEPTR with the Ice King's ice powers. After this, Ice King explained to Finn that after he zapped NEPTR with his ice power, he was became infused with the Ice King's private particles, which also became his "son". They interacted with each other again in "Mystery Dungeon", where they will be working together, along with Tree Trunks, Shelby, and Earl of Lemongrab. For the most part, NEPTR tried very hard to gain his "father's" affections and was greatly disappointed when Ice King had forgotten him. He got his feelings hurt when it was revealed that Ice King had kidnapped the group and had accidentally picked NEPTR. He, though unintentionally, blurts that he had wanted Beemo instead and not NEPTR. However, NEPTR is still loyal to him and forgives him after they escape the dungeon. When he sees Ice King disappointed that he couldn't bring his fanfiction to life; NEPTR reminds him to use his imagination the same way that he tried with NEPTR.

Tree Trunks
NEPTR and Tree Trunks never interacted with each other until "Mystery Dungeon" where they will be working together, along with Ice King, Shelby, and Lemongrab. Although, he got a little jealous of her because she makes pies and everyone thinks she's the only one who could make pies when he also could.

Earl of Lemongrab
NEPTR and Lemongrab never interacted with each other until "Mystery Dungeon" where they will be working together, along with Ice King, Shelby, and Tree Trunks.

Shelby
NEPTR and Shelby never interacted with each other until "Mystery Dungeon" where they will be working together, along with Ice King, Lemongrab, and Tree Trunks.

Flame Princess
Neptr never really interacted with Flame Princess except he nearly killed her by thinking she was a goblin on fire and was about to extinguish her.

Episodes featured

 * "What is Life?"
 * "Hot to the Touch"
 * "BMO Noire"
 * "All the Little People" (toy)
 * Mystery Dungeon

Trivia

 * In the end credits for "What is Life?," Neptr is listed in the credits as "N.E.P.T.E.R."
 * It is unknown where Neptr gets the ingredients for the pies he makes, possibly generating them spontaneously through magic rather than machinery.
 * Neptr is like the monster from Mary Shelley's Frankenstein as both are brought to life by lightning and are made from salvaged non-living parts.
 * In a sneak peek of "Hot to the Touch," Neptr's name was spelled "Neptor" which is his name in the Spanish version of the show.
 * "Hot to the Touch" contains Neptr's first song, "Working for the Master."
 * He was one of the little people (seen near the end when they're all dancing) in "All the Little People."
 * Though he is a robot, everyone considers him male (as opposed to BMO, who is genderless but called male and female by different people).