The Chaos Emeralds are seven gems of enormous power at the centre of the Sonic the Hedgehog games. Gather all seven and Sonic turns into Super Sonic, a golden form that enemies cannot hurt; in the wrong hands they power doomsday machines. Shadow the Hedgehog is the black hedgehog built fifty years before Sonic Adventure 2 to be the Ultimate Life Form, and he uses the emeralds to bend time and space with Chaos Control. Knuckles guards the Master Emerald, the larger stone that keeps the seven in check, and Tails is Sonic's two-tailed fox sidekick and mechanic.
The series has run since 1991 and been retold in comics, cartoons and films, often with changes. This sticks to the main games and names the game behind each claim. Every design on the Sonic shelf comes from this cast. Spoilers for Sonic Adventure 2 below.
What the Chaos Emeralds are
The first Sonic the Hedgehog (1991) had six Chaos Emeralds, won in its special stages. Sonic the Hedgehog 2 made it seven, and seven it has stayed. Each one is a store of energy that can power a machine, warp space or, gathered together, change whoever holds them.
Dr Eggman (called Dr Robotnik in the early Western releases) spends most games trying to plug the emeralds into his machines, and Sonic spends most games stopping him. That is the series' basic plot, and it has barely moved in thirty-odd years.
Sonic Adventure sets out the rule the later games follow: the emeralds' power answers the heart of whoever uses it. Fed by rage, the seven turn a water creature called Chaos into Perfect Chaos, which floods Station Square. Turned to good by Sonic's friends, the same seven make Super Sonic, who beats it.
Super Sonic and Hyper Sonic
Super Sonic first appears in Sonic the Hedgehog 2 (1992). With all seven Chaos Emeralds and at least 50 rings, Sonic jumps and turns gold: his quills lift, he gets faster and enemies can no longer hurt him. The catch is fuel. The form burns one ring a second, and when the count reaches zero he drops back to blue.
Sonic 3 & Knuckles (1994) adds a step up. With all seven Chaos Emeralds, a giant ring takes Sonic to the Hidden Palace, where the Master Emerald's shrine turns them into seven grey Super Emeralds, each brought back to life by clearing a special stage. With all seven Super Emeralds he becomes Hyper Sonic, who flickers through colours and can wipe every enemy off the screen with one flash.
The 3D games save the form for final bosses: Super Sonic against Perfect Chaos in Sonic Adventure, and Super Sonic beside Super Shadow against the Finalhazard in Sonic Adventure 2. Speed Shop puts Sonic himself on the back.
Shadow the Hedgehog's origin
Shadow's story is told in Sonic Adventure 2 (2001) and filled out in Shadow the Hedgehog (2005). Fifty years before the first of those, Professor Gerald Robotnik, Eggman's grandfather, runs Project Shadow aboard the Space Colony ARK, a research station in orbit, to build the Ultimate Life Form: a being that will never die.
The result is Shadow, a black hedgehog with red streaks who skates on hover shoes. His only friend on the ARK is Gerald's granddaughter, Maria. When G.U.N., the military, storms the colony to shut the project down, Maria pushes Shadow into an escape capsule and sends him to Earth, and she is shot. Gerald is imprisoned and later executed.
G.U.N. keeps Shadow sealed in stasis in a facility on Prison Island. Fifty years on, at the start of Sonic Adventure 2, Eggman breaks in, finds his grandfather's creation and wakes him. Shadow remembers Maria, but her last wish has twisted in his memory into revenge on the planet.
Shadow the Hedgehog adds the last piece: Gerald made him with the help of Black Doom, leader of the alien Black Arms, using Black Doom's own DNA.
Chaos Control and the fall of the ARK
Chaos Control is the technique that uses a Chaos Emerald to warp time and space. In Sonic Adventure 2 Shadow uses it to vanish and reappear in an instant, and Sonic copies it with a fake emerald Tails built, to escape when Eggman fires him off the ARK in a pod rigged to explode. Shadow Generations (2024) makes stopping time a move you play. Chaos Control is named for it.
In Sonic Adventure 2, Shadow helps Eggman gather the emeralds to fire the ARK's Eclipse Cannon. Slotting in the last of them sets off Gerald's final program: the ARK starts falling towards Earth. Amy reminds Shadow what Maria actually asked of him, to help the people down there, and he and Sonic go Super to beat the Finalhazard and push the colony back. His power spent, Shadow falls towards the planet and is presumed dead.
He is back in Sonic Heroes (2003) with no memory, teamed with Rouge the Bat and the robot E-123 Omega as Team Dark.
Knuckles and the Master Emerald
Knuckles the Echidna debuts in Sonic the Hedgehog 3 (1994) as guardian of the Master Emerald on Angel Island, a land mass that floats in the sky because of it. Eggman crash-lands there and tells Knuckles that Sonic is after the emerald, so Knuckles spends the game ambushing him. In Sonic & Knuckles he learns the truth and joins the fight. He glides, climbs walls and breaks through rock, though he cannot jump as high as Sonic.
The Master Emerald is the controller: it can cancel out the power of the seven. Sonic Adventure gives its history. Knuckles' ancient echidna ancestors, led by Pachacamac, tried to seize the Chaos Emeralds; Chaos, the guardian of the emerald shrine, wiped them out, and Pachacamac's daughter Tikal sealed herself and Chaos inside the Master Emerald. Eggman shatters it at the start of the game to free Chaos, and Knuckles spends the story finding the pieces.
In Sonic Adventure 2 he breaks it himself, rather than let Eggman and Rouge take it. Team Up pairs him with Tails.
Tails, Amy and the rest of the crew
Miles "Tails" Prower is a young fox with two tails who first appears in Sonic the Hedgehog 2. He follows Sonic everywhere, flies by spinning his tails like a rotor and, in Sonic 3, can carry Sonic through the air. He is the team's mechanic and pilot, flying the Tornado biplane in Sonic 2's Sky Chase stage. In Sonic Heroes, he, Sonic and Knuckles are Team Sonic.
Amy Rose first appears in Sonic CD (1993), where Metal Sonic kidnaps her. In Sonic Adventure and after, she fights with her Piko Piko Hammer and is set on marrying Sonic, who keeps running.
The Moto Edition run gives five of the cast a cover each: Sonic, Shadow, Knuckles, Tails and Amy Rose.
On the back of a tee
The whole crew is on the Sonic shelf, drawn from canon reference art. Check the size guide before you pick a size.
Why it works on the back: every character is one strong colour and one shape (blue quills, red fists, two tails, black and red stripes) built to be read at full speed on a small screen, so it reads just as fast from across a room.
Read next: The Triforce, Majora's Mask and the Zelda timeline explained (three golden triangles instead of seven emeralds) and Pokémon types, evolution and legendaries explained.
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