mulish

Extremely or irrationally stubborn and intractable. synonym: obstinate.

Resembling a mule.

Like a mule; having the characteristics of a mule; sullen; stubborn; also, of a hybrid character.

Like a mule; sullen; stubborn.

Characteristic of a mule; stubborn, obstinate, or intractable

unreasonably rigid in the face of argument or entreaty or attack