Be is an extremely irregular composite verb. It is made up of three verbs, is (am, are, art), be, and was (were).

Indicative
Present Past
I am I was
You are You were
He is He was
We are We were
You are You were
They are They were
Subjunctive
Present Past
I be I were
You be You were
He be He were
We be We were
You be You were
They be They were

Chapter VII
SENTENCE CORRECTNESS

The language spoken and written by educated persons and by trained writers in all parts of the English-speaking world has certain forms and usages to which everyone must conform if he wishes to be recognized as a well-educated man or woman. Conformity to the word-forms and to the sentence structure of this widespread language is called correctness.

300. Use the nominative case for the subject of every finite verb. I, thou, he, she, we, they, who, are nominatives.

Wrong. Him and I graduated last year.

Right. He and I graduated last year.

Revise. Us and her went by ourselves.

301. Use the nominative form who for the subject, even if a parenthetical he says, he thinks, etc., intervenes between subject and verb.