Am, is, and was are used with singular subjects. Am is the 1st person present tense; is is the 3rd person present tense; was is the 1st and 3rd-person past tense.
Present: (1st person) I am late. (3rd person) She is late. He is late. It is gone.
Past: (1st person) I was late. (3rd person) She was late. He was late. It was gone.