Brain often claims Pinky to be the main failure of his plans, although in actuality these failures were sometimes not Pinky's fault.
Pinky is often silly, dumb, insane, lovable, funny, open-minded, sweet, kind-hearted, polite, sensitive, gentle, child-like, joyful, patient, naive, friendly, loyal and cute. Despite the pain and insults he took from his fellow roommate, he was almost always happy and giddy. However, there were a few times that these factors of the character were changed. In the episode "That Smarts" it is revealed that when he becomes very smart, Pinky's realtionship with Brain loses all of it's interest and it becomes boring. However, to his credit Pinky does know all of the names to all of the world's cheeses and can even name what country produces each type of cheese. Pinky also once almost convinced all of the rulers of their countries to hand-over their countries to Brain as part of his birthday gift (Pinky even managed to keep the secret from Brain, but it only made Brain wonder what Pinky was up to and led him to ruin his own birthday). Surprisingly whenever Brain's intellectual methods didn't work (which was very rare), Pinky's instincts kick in and usually do a good job of guidance. There's even been a few cases where Pinky provided great useful knowledge about certain topics like comic books. In the episode titled The Pink Candidate, it showed that if Pinky were to become President of the Untied States than he would be a fair, loyal and honest leader. This loyalty to Brain has also shown it's self in many other cases. An example of Pinky's loyalty to Brain would be found in the epsiode "Snowball" where Brain's enemy Snowball tried to sway Pinky into believing that Brain was just using him. Pinky however, was unswayable and refused to believe Snowball.