Jake the Dog

Jake the Dog is a fictional character and one of the main cast in the American animated television series "Adventure Time" created by Pendleton Ward. He is voiced by Billy West. 
The character made his debut in the original pilot. Jake is Finn's best friend and adoptive brother. He is a shape-shifting dog who is in his 30s in "magical dog years". Jake can stretch, shrink, or mold any part of his body to any shape and almost any size, ranging from becoming gigantic to becoming incredibly small.
Jake has a laid-back attitude in most situations, but loves adventure and is in a relationship with Lady Rainicorn voiced by Niki Yang; they have five children together.
The character has received largely positive critical reception.