Jake The Dog.

Jake (full title: Jake the Dog), the deuteragonist of Adventure Time, is a magical dog and Finn's constant companion, best friend, and brother by adoption. Jake has Stretchy Powers, which allow him to stretch and manipulate his body, coming in handy on innumerable occasions throughout his and Finn's adventures. He is the son of Joshua and Margaret. Jake has a brother named Jermaine. Jake is 28 in magical dog years,but he rarely acts maturely. He is probably 14, around Finn's age, in human years. Both he and his girlfriend, Lady Rainicorn, share a passion for playing the viola.