Thumper

Thumper is a red quarry machine with two arms and caterpillar tracks, who was designed and bought for loosening rocks and enabling the workman to collect it faster. He proved useful, but often went out of control, which caused a huge boulder to run loose and chase the narrow-gauge engines down the line. These days he is mainly used for slate mining.

Thumper has had no real personality, although he has been said to act as a 'cool man'. He only featured in one Season 5 story, 'Rusty and the Boulder', with no dialogue. He was the first non-Awdry character created with caterpillar treads.

He is not based upon any particular type of quarry machine - indeed, a machine of that sort would be positively dangerous to those around. Another example would be the lack of windows at the front of the cab, making the operator unable to see.