Some transitive verbs can be followed by an object together with an adjective or a noun phrase that gives more information about the object. This adjective or noun phrase that complements the object is called an object complement.

She made me angry. (Here the adjective angry is the complement of the object me.)
You are driving us crazy. (Here the adjective crazy is the complement of the object us.)
They appointed him monitor. (Here the noun monitor is the complement of the object him.)
I found his attitude strange.
Don’t call me a liar.
They painted the wall green.
The noise drove him mad.
That case made the lawyer famous.
We find the cost of living in cities rather high.

Verb + Object + As + Complement

Note that after some verbs the object complement is introduced by as. This is common when we are describing somebody or something.

They elected John as their leader.
I regard him as a genius.

She described her attacker as a tall dark man.

Note that the structure is also possible with as being.

We do not regard him as being dangerous. OR We do not regard him as dangerous.

Verb + object + to be + complement

Verbs such as believe, consider, feel, know, find, think, prove, understand etc., can be followed by object + to be + adjective/noun phrase.

Events proved him to be wrong.
Most people supposed him to be innocent.
I considered the plan to be unwise.
I knew him to be conscientious.

Note that in an informal style, these sentences can be re-written using that-clauses.

Events proved that he was wrong.
Most people supposed that he was innocent.
I considered that the plan was unwise.
I knew that he was conscientious.