What is the name of Groundskeeper Willie's tractor in "The Simpsons"?

William (Mr) AKA Groundskeeper Willie -- The school caretaker. A Scotsman with a love for his tractor "Agnus". Does not like Principal Skinner. Was a member of the Springfield Stonecutters. Member of the Stereotypes bowling league team.

tim.rawle.org/simpsons/cha_rz.htm [no longer exists]

I was checking to see if that was supposed to be "Angus" rather than "Agnus" and although there are a few references each for both Angus and Agnus, I also found this:
Willie often drives a tractor called "Duchess", the make of which is also a Willy.
https://en.wikipedia.org/wiki/Groundskeeper_Willie

Who Shot Mr. Burns? Part Two
- Willy (riding his tractor Dutchess)
At the sun-blocking machine, several vehicles pull at it with ropes. Otto drives the school bus, Snake, an ATV, Chespirito, the KMEX TV van, and Willy, his tractor. "Pull, duchess, pull!" he exhorts. They manageto break it free. It falls down the side of the hill onto a town on the other side amid much crashing and screaming.
https://www.simpsonsarchive.com/episodes/2F20.html

It is spelled both ways, Dutchess and duchess, at the reference site.