- "In fact, once he got so into it, he almost made a Boulder crush every engine known to man... It was really bizarre."
- ―Diesel 10, Rock-Star
Thumper is a cool, red collected Quarry Machine designed for clearing rock.
Thumper first came to the island during the construction of Boulder Quarry, and was intended to be used to help collect rock faster. However, there was a large spherical boulder within the quarry hanging precariously over a ledge, and after a heavy rainfall loosened the rock, Thumper accidently caused the boulder to crash down and essentially ravage the narrow guage lines and the new quarry, which was closed shortly afterwards. After this, Thumper was mainly used for slate mining.
However, when The Flying Scotsman was trapped by a rock slide and Diesel 10 was unable to clear it, the latter suggested that Thumper be used to help clear the rock slide, which Thumper did easily, being brought over by Sidney.
Thumper is extremely enthusiastic about his line work, very much enjoying crushing rock. However, it can get to the point where things can get out of control. When he is not slate mining, he can be described as having a "cool man" personality.
Rusty can be quite nervous around him after a boulder almost crushed him.
- Season 1: The Old Warrior (cameo)
- Season 2: Mavis and the Tornado (cameo), Rock-Star, Blunderbuss, Swan Dive (cameo), Luke and Millie's Blue Mountain Adventure, All the World's a Stage (cameo), Swashbuckler (flashback cameo)
- In an interview, EE93 stated that Thumper's voice actor resembles the actor Bill Murray.