Thumper is a quarry machine with two arms and caterpillar treads. He is used for loosening rocks.
Thumper was built by to Sodor Mining Company and brought to the quarry to help clear rock, but his arms accidentally dislodged an enormous boulder which chased Rusty, Skarloey, and Rheneas down the line before nearly crushing Percy and running into the sheds at the mine. He often got out of control on mining sites and is now used for slate mining.
Thumper has been said to be laid back in his approach with a "cool dude" attitude, though he can come across as accident-prone.
Thumper is not based upon any known quarry machine - at any rate, a machine of his type would be extremely hazardous to those around due to the lack of a window at the front of the cab, making the operator unable to see.
Thumper is painted orange-red with his name painted on his side of his bonnet in white.
He also appears briefly in the PC game Building the New Line where he clears rocks when they fall onto the tracks.
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