He is extremely intelligent but proud.

Intelligent : having or showing intelligence, especially of a high level.
Simple : easily understood or done; presenting no difficulty.
Ignorant : lacking knowledge or awareness in general; uneducated or unsophisticated.
Weak : lacking the power to perform physically demanding tasks; having little physical strength or energy.
Dull : (of a person) slow to understand; stupid.

Antonym of Intelligent is Dull