In the sentence 'The governor, together with his aides, was received at the airport', the subject of the verb 'was received' is ________.

The phrase 'together with his aides' is a parenthetical addition set off by commas and does not form a compound subject. The true grammatical subject of the sentence is 'the governor' (singular), which is why the singular verb 'was' is correctly used. 'Together with', unlike 'and', does not join subjects to form a plural compound subject.