Mrs Creecher is Dennis's teacher at Bash Street School.
Nobody's sure how old Mrs Creecher is, but one of JJ's brothers says she taught Winston Churchill his ABC's, and another says the first apple left on her desk came from a boy called Adam.
She might be a teeny-weeny bit short-sighted, because she can't tell that Gnasher sneaks into class every day by pretending to be Dennis's backpack.
The first thing she loves is homework.
Mrs Creecher thinks all homework is a Good Thing, and you can never have too much of a Good Thing, right?
How wrong can one person be?
Mrs Creecher's book of school rules dates back to mediaeval times, and has rules in it that use words like 'forsooth' and 'urchin' and 'treason' - yikes!
Mrs Creecher can remember every single rule in her book, which means she knows more than 10,000 things that Dennis isn't allowed to do!