Ouroboros is a family of proof-of-stake consensus protocols used in the Cardano and Polkadot blockchains.
[1] Ouroboros was published as "the first provable secure PoS consensus protocol".
It was postulated by an academic team led by Aggelos Kiayias at the Annual International Cryptology Conference in 2017.
[2] Later that year, Ouroboros (Classic) was implemented by IOHK as the basis of the Cardano blockchain platform and various upgrades.
[4] Nguyen et al. compared Ouroboros to other PoS protocols.