Grasscutter

It's only been 9 days since the grass in the park was last cut, but here he is at it again.
He appears on his huge mower, clad all in black and manoeuvring the behemoth of a machine with purpose. It looks like a Transformer. Maybe it is?
He speeds up and down, not caring for a nice striped effect and leaving piles of freshly-murdered grass in his wake.
He disappears out of the park and away up the road once he's finished the hatchet job.
The council guys arrive soon after with a mower of their own, baffled that the job has already been done.
Who is the grasscutter?