After some verbs the direct object can be followed by an object complement – a noun or adjective which describes or classifies the object.

• They elected him their leader.
• The other children called her stupid.
• We all regarded her as an expert.
• Queen Victoria considered him a genius.

When these clauses are made passive, these objects complements become subject complements; they come after the verb.

• He was elected their leader.
• She was called stupid by the other children.
• She was regarded as an expert.
• He was considered a genius by Queen Victoria.