Au/Ahau means: Me.
au/ahau are commonly used interchangeably based on what fits the rere/flow of the sentence, although Northern dialects will tend to use ahau vs au which is more common elsewhere. ‘wau’ and ‘awau’ are other dialectal variants you might come across.
Pronouns in te reo Māori are used the same way as personal nouns. They take the personal article ‘a’ when used after the prepositions i, ki, kei and hei as in:
The key difference between au/ahau is in their use with this personal article. The ‘a’ is omitted if ‘ahau’ is used:
It’s considered likely that ahau is derived from ‘a au’. The inserted ‘h’ is a thing called epenthesis.
Another good thing to be aware of with au/ahau is that when the personal article ‘a’ is used before the singular pronouns au, koe or ia, the ‘a’ is often pronounced long and is the stressed part of the sentence.