I couldn't find it is the phrase.
He has a great mind, passion in the field of art and tactician skills, because of this, he was perceived to be gifted. Brutus underestimated him because he was a person who does not take life seriously and his ability to be an orator.
Not influence by, <span>showing, or involving personal feelings
or
</span>
<span>not existing as a person; having no personality</span>