Ring

One distinctive and recurring feature of Sonic games are the collectible golden Rings (sometimes referred to as Gold Rings or Power Rings) spread throughout the levels. This gameplay device allows players possessing at least one ring to survive upon sustaining damage from an enemy or hazardous object. Instead of dying, the player's rings are sacrificed; in most Sonic games, a hit will cause the player to lose all of their rings, although in certain situations (such as the Special Stages in Sonic the Hedgehog 2) and throughout certain games (such as Sonic Triple Trouble, Shadow the Hedgehog, Sonic and the Secret Rings, Sonic Unleashed, and Sonic Blast) a hit only costs a set number of rings rather than the entire collection. In more recent games, usually only 20 rings are now lost.

Game Mechanics
As mention above, rings are spread plentiful throughout the levels in the Sonic series and can be collected upon contact. Possessing rings allows the playable character to survive attacks or impacts with enemies or any dangerous obstacles, such as spikes, fire pits ect, that would otherwise cost the player a life. As long as the player is in the possession of at least one ring, they can avoid most lethal attacks. Upon colliding with a hazard, the on-screen character is thrown backwards and given a momentary period of invulnerability (represented by a rapid flashing between visible and invisible). The dropped rings burst out of the character in a circular pattern and bounce around the environment, flashing for a few seconds before disappearing entirely. During this brief period, it is possible for the player to recover some of the rings they lost. Generally fewer "recoverable" rings are displayed on-screen than the number actually lost (usually a maximum of around 20; fewer in Sonic games on 8-bit consoles, about 50 in Sonic Rush, while in the Sonic 4 saga the player can recover about 35). If the player suffers damage without possessing any rings, the player will lose a life.

Certain causes of death cannot be prevented by holding a ring, including being crushed, falling into a bottomless pit, failing a mission held through a time limit and drowning.

In line with many platform games, collecting 100 of these common collectibles will usually reward Sonic with an extra life. Certain titles in the series often reward the collection of other quantities of rings, often in conjunction with the Chaos Emeralds; usually, at least fifty Rings are required to access the Special Stages in which the Chaos Emeralds may be obtained, or to utilize a character's super transformation.

The origin of the rings, like the Chaos Emeralds, is never revealed during the game series. In addition, even Sonic characters are shown to have thought they came from a different world in official media. They are not often referenced by characters during gameplay, but they are used as currency in Chao Black Markets and in shops in Sonic the Hedgehog (2006) and Sonic Chronicles: The Dark Brotherhood. They are also mentioned to be a monetary system in Sonic Heroes. In Shadow the Hedgehog, Dr. Eggman collects them for prizes in his game-filled carnival base, and is distressed when Shadow takes them from him during the "Egg Dealer" boss battle. Rings can also be used to buy Extreme Gear in Sonic Riders and Sonic Riders: Zero Gravity.

Other continuities
Rings are also canonically equipped to characters throughout the media. To Spin Dash in any cartoon, contrasting to all the games, Sonic must have a power ring and can only collect one at a time. In the SatAM cartoon, Sonic also comments that the rings only last for 24 hours and work only for him. Amy and Shadow also wear rings on a daily basis, Amy probably to protect herself, and Shadow to retain his abilities (they have been with him since his creation).

Archie Comics
Power Rings are natural byproducts of Chaos Emeralds, though they do not contain the limitless power the Chaos Emeralds do. Power Rings were artificially created by the brilliant Overlander scientist Nate Morgan as a clean alternative to fossil fuels to protect Mobius' environment. Also, Sonic's Uncle Chuck and Tails are shown to create rings. After Morgan's banishment from his home city, when his original tests failed, the Mobian Sir Charles Hedgehog aided him in mass producing Power Rings to be used by the Kingdom of Acorn. Following this, the city of Mobotropolis entered a new Golden Age as the Power Rings had brought their kingdom out of the medival ages. Since then, Power Rings have been used not only as power supplies for technology, but also as a means to increase the power and capabilities of certain individuals such as Sonic the Hedgehog, Miles "Tails" Prower and Knuckles the Echidna.

History
Many years before the Great War, Nate Morgan was the head of a team of underground scientists in the city of Megapolis which were studying to create a clean alternative for the fossil fuels that had been polluting the Overlander cities for years. One of the science team members, Julian Kintobor, sabotaged the calibrations of one of the early prototypes and encouraged the unsuspecting Nate to go ahead with the test. Due to Julian's tampering, the test resulted in a massive explosion, which would later cause Nate to be banished from Overlander territory forever. (StH: #65)

While wandering in exile, Nate Morgan was located by the current monarch of the Kingdom of Acorn - Frederick Acorn. The king offered his hand of friendship and brought Nate back to the kingdom where he became very close with the royal family. Finally, using the energies within a Chaos Emerald, Nate was able to properly test and perfect the Power Ring and create it as a new energy source. Following this, the Kingdom of Acorn, which had remained as a per-industrial state for centuries due to the Mobians wishing to preserve nature, rebuilt Mobotropolis as a post-industrial city booming with technology run on the energy of the Power Rings. (StH: #65)

After a plot by Kodos and Ixis Naugus to have Nate banished from the kingdom, Nate imposed self-exile, feeling he had brought too much trouble to both the Overlanders and Mobians. Realizing the technology of the Power Rings could be used for evil if Kodos or Naugus got their hands on it, Nate brought the sole Ring Forge with him when he left. While wandering through the Great Forest, Nate stumbled upon a hollow stump and decided to bury the Ring Forge beneath a lake near the hollow stump he fell through. This was what produced the Power Rings used by Sonic and the Knothole Freedom Fighters in Knothole years later during their war against Dr. Ivo Robotnik. (StH: #65)

Use by Mobians
During their war against the despot Dr. Ivo Robotnik, the Power Rings aided the Knothole Freedom Fighters by providing their main fighter Sonic to increase his speed and other capabilities. After finding himself in an alternate zone, Sonic discovered that by collecting fifty power rings and seven Chaos Emeralds he could achieve a super transformation of himself called Super Sonic. In this form, Sonic was virtually invulnerable and his powers were dramatically increased. In his Super Sonic form, Sonic managed to make short work of Universalamander. (StH: #4)

When Sonic gathered his One Billionth Power Ring he was transported to a unique zone where he found himself face to face with the Ancient Walkers. The ancient gods felt that Sonic gathering one billion rings was a milestone worth rewarding. Thus, after putting Sonic through a series of tests, the Ancient Walkers empowered Sonic's One Billionth Power Ring with more energy than any other. (StH: #35)

Since then, Power Rings have been used for numerous purposes. Dr. Ivo Robotnik gathered and used a large number of them to power his massive aerial weapon known as the Death Egg. The Freedom Fighters also used the immense magical powers of the power rings to stop the process of King Max's crystallization, though the Power Rings merely slowed down the process. (SQM: #1, #2, #3, SvK)

When used by someone pure of heart, a Power Ring can temporarily enhance an individuals natural abilities for a short time period. Antoine D'Coolette demonstrated this facet of the rings when he used one to cut through a pursuing Eggbot with his sword in a single swing. (SSS: #1)

Of the less noble beings to utilize them, Monkey Khan made use of a Power Ring he found in a trench shortly after release from the crypt he was sealed in by Princess Sally Acorn and made a crown out of it which greatly increased his own powers and enabled him to summon lightning. A sorceress known as the Iron Queen, also used Power Rings to amplify her spell-casting enough to bewitch Monkey Khan and make him fight Sonic and Tails during their pursuit of Naugus.(StH: #55, StH: #60)

Power Rings have also been successfully employed by beings other than Sonic or Robotnik's machines. Both Jules and Bernadette Hedgehog had wedding bands fashioned out of Power Rings and housed on their arms when both were still Robians. This allowed them both to retain their free will after Robo-Robotnik regained control of all the other Robians, similarly to what had occurred with Mecha Sonic. (StH: #39, #73, #75)

After being mortally wounded by an imposter Tommy Turtle that was really an Auto Automaton, Jules was saved when Sonic used a ring he acquired from the Lake of Rings nearby and wished for it to heal his father. (StH: #136)

Adventures of Sonic the Hedgehog
In an episode of Adventures of Sonic the Hedgehog, called "The Mobius 5000", the Power Rings were just like the rings in the games.

SatAM
In the SatAM series, Sir Charles Hedgehog, created the Power Rings for Sonic to temporarily boost his speed. Sir Charles built a machine, powered by a special rock to generate the rings. It is currently at the bottom of a lake in the Great Forest. One ring rises to the surface every day, and if not caught, it sinks back underwater.

Sonic the Comic
In Sonic the Comic, the Golden Rings are an apparently naturally-occurring phenomenon of Planet Mobius. They were used by Doctor Ovi Kintobor in conjunction with his Retro-Orbital Chaos Compressor (ROCC) to transfer most of the evil energy on Mobius into six Chaos Emeralds. They possessed strange properties (possibly inherently, or possibly as a result of their use in the ROCC) and emitted special Ring Energy. Robotnik was able to use the rings to power his Neutrino Accelerator. According to Tails, this Ring Energy was also responsible for Sonic's first transformation into Super Sonic, although Sonic had absorbed so much Ring Energy over the years that later transformations were caused purely by stress.

During the explosion of the ROCC, Kintobor's personality was once somehow imprinted on a Golden Ring. Porker Lewis was able to use this ring to create the Kintobor Computer.

Larger versions of the Golden Rings, known as Mobius Rings, which lead to other dimensions such as the Special Zone, are located all over Mobius.

Sonic X
In Sonic X, the rings are a little smaller than their SatAM counterparts, but they function in a similar fashion.

Tails uses rings on X-Tornado, probably as energy source. He also stores rings in order to give them for Sonic, who could then use their energy boost to destroy enemies faster.

Trivia

 * Rings never made an appearance in the show Sonic Underground.
 * In Sonic X, the rings play a different role: not only do they enhance Sonic's strength, but they also weaken enemies in the form of the Ring Tunnel.
 * Interestingly, the rings shown in the games do not have such powers, only that they can prolong Super Sonic's de-transformation and after 50 are gathered trigger such transformation (after collecting all seven Chaos Emeralds.)
 * In SatAM, a Power Ring can be used to temporarily free a roboticized person.
 * The familiar sound effect used for rings has been adopted for use in cash registers.
 * Rings can also have other purposes. For example, Shadow's Inhibitor Rings keep his powers in check as long as he wears them.
 * The Sonic Storybook Series (starting with Sonic and the Secret Rings) is the first time a Sonic game has had the rings replaced with something else. In Sonic and the Black Knight, they were replaced with namely fairies. However, rings still appear in the Legacy missions in this game.
 * In Sonic Colors(Wii version only), unlike the rest of the Sonic games, the player is not awarded an extra life if he/she collects 100 rings.
 * In the Sega game Bayonetta, rings pop out of enemies after being defeated, particularly, basketball size gold rings. This is in opposition to the Sonic series as the rings pop out of the player's character after suffering a hit by an enemy.
 * A joke was made in Sonic Generations in which both Classic and Modern Tails were discussing about how many rings Sonic collects and where he puts them.
 * It's possible that the rings in the games are made up of an unknown energy source due to their numerous powers.