This paper model is Neptr (or N.E.P.T.R., an abbreviation for Never-Ending Pie-Throwing Robot), a pie-throwing robot Finn created solely to prank Jake who first appears in "What is Life?" of the American animated television series Adventure Time, the papercraft is created by WebDude.
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. Neptr speaks in an electronically filtered upbeat but stilted voice. He usually calls Finn "creator" and the Ice King "Papi."
He came to life when Finn became frustrated that his shoddily-assembled "robot" was not 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 is not 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 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 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. [Source: wikia]