Roller

Roller, known as Arma (アルマ) in Japan, was badnik created by Doctor Robotnik. It has only appeared in the original Sonic the Hedgehog, being one of Robotnik's first creations that could keep up with Sonic the Hedgehog.

Physical Appearance
Roller is blue colored, round-shaped badnik which has above the body has red spike that is divided into the two ends. The badnik has interesting design as the above part of the body is actually upwards opening hatch, which reveals paired of eyes and small gray hands. It also reveals two mechanical feet and sharp tail. All these little parts hide in the body, as the badnik will changes its shape to the ball and came back after that.

Abilities
The badnik's signature ability has been to roll into ball and travels at high speeds with the intention of plowing through their prey. One screen is not simply enough to notice the Roller, as these badniks can come any moment behind its victim with its high speed.

Sonic the Hedgehog (1991)
Roller's only game appearance has been in the original 16-bit version of Sonic the Hedgehog, as it can be found from Spring Yard Zone. It is the most easily defeated when it stops to open their casing to check the surroundings, but can be defeated with a Spin Attack whilst moving (albeit with some difficulty).

Rollers have a tendency to plow through Sonic right when he least expects it, but the player should be particularly wary when crossing areas with steep hills nearby as these places are where Rollers are more common.

Sonic the Comic
In Fleetway's Sonic the Comic, a kindhearted Roller badnik (named, simply, "Badnik") once befriended a young boy named Smokey. Sonic allowed the Roller to survive when Smokey begged the hedgehog to let it go.

Adventures of Sonic the Hedgehog
Roller have also appeared in Adventures of Sonic the Hedgehog episode Untouchable Sonic. Roller's design in the series is significantly different with the exception of his head as it resembles more of a long-necked lizard with business suit which can transform to the bowling ball.

Ballhog and Roller are part of Dr. Robotnik's Or Else Protection Service, where they bully Mobians into paying them to not destroy their business. They are easily defeated by Sonic. Later at the end of the episode, Tails had converted Ballhog and Roller's remains for an attraction for Bert's Diner.

Archie Comics
Roller appears briefly in Archie's Sonic the Hedgehog comics' issue 18. Roller was part of team which also has Crabmeat, Buzzbomber, Newtron, Coconuts and Slicer, as all of them were sent by Robotnik to ruin the wedding of Sonic the Hedgehog and Sally Acorn. However Roller along with other badniks got easily defeated as the wedding revealed to be part of a play.

Trivia

 * As the Spring Yard Zone was originally called "Sparkling Zone", Roller badnik was showed to be purple colored instead of blue.
 * In Spring Yard Zone, for odd reason Roller's sprites may start to get messed up, which reveals to be graphical glitch in the game. This can happen if the player keeps following it for while.
 * As being the first badnik to keep up with Sonic the Hedgehog, it is possible that the badnik is based on the hedgehog himself due its design and moving fast. The badnik cames before many other robotic Sonic clones.
 * It seems that Roller is cable to performing Spin Jump, as they do this from a short distance and then disappear from the screen. However this hasn't never been officially confirmed.
 * It can be noticed that Roller has similar looking legs as Ball Hog and Bomb in artwork illustration.
 * Roller is one of badniks (with Bat Brain) that hasn't made appearance in the 8-bit version of Sonic the Hedgehog, since Spring Yard Zone doesn't appear in 8-bit version. Unlike Bat Brain, none of Roller's sprites aren't found from game's data.
 * Roller also is one of badniks from the original Sonic the Hedgehog that hasn't made any game appearance since then. You may think it would be useful for Robotnik.
 * The Roller's head in Adventures of Sonic the Hedgehog is very similar in appearance to a Soarar in Kirby Mass Attack.