Euclideans are a species from the animated series Gravity Falls. They are two-dimensional, geometric beings from the dimension Euclydia. The species, along with their home dimension, was wiped out and destroyed by the series’ main antagonist, Bill Cipher. Despite being a Euclidean himself, Bill Cipher was born with a rare mutation that allowed him to view the third dimension. Other Euclideans had no concept of the direction “up” and could only see and move within a completely flat plane of existence.