Sir Slicer is a villain from Adventure Time who appears in "Blood Under the Skin".
He is voiced by Peter Stormare.
Sir Slicer appears when some knights start laughing at Finn because of his thimble. Sir Slicer mocks Finn for having no armor then continues mocking him throughout his whole journey to get the Armor of Zeldron. First he calls Finn "Crimsons Checks" after Finn got shocked and embarrassed from seeing several naked people showering in the Swamps of Sadness, Then he makes a barb sing an embarrassing song about Finn after a Red-Faced Monsters mistakes him for her baby. He claims grandfathers will sing the song to their grandchildren for generations which Finn debunks. The Red-Faced Monster tries to attack him in retaliation but is blocked off by hiss armor, he then grabs the barb and leaves on his horse.
In the end of the episode Sir Slicer still mocks Finn because he still has no armor then he mocks Jake for being dressed like a lady. However Finn mocks Sir Slicer for wasting his time following him and challenges him to a fight. However, when he tries to move he falls off his horse due to his heavy armor. He tries to get back up with the use of a stick but get a splinter just by touching it. Finn then trows a thimble at him then leaves him on the ground.
In "Gumbaldia" He is one of the many villains teaming up with Gumbald to go to war with the Candy Kingdom.
- Sir Slicer made an appearance in Sound Castle 2. It takes three hits (one of each color) to take him down.
- Slicer's voice actor, Peter Stormare, is also known for lending his voice to several video game characters such as Mattias Nilsson; a Swedish mercenary from the video game titles Mercenaries and Mercenaries 2: World in Flames.
- Sir Slicer is a parody of Baron de Ghost (original name: Danshaku), the villain in the 1981 film The Fantastic Adventures of Unico based on the manga characters of Osamu Tezuka.
- Sir Slicer's horse seems to be very strong; it can carry the weight of Sir Slicer's armor.