Bitcoin is the first and most famous cryptocurrency, created in 2009 by someone called Satoshi Nakamoto. Its unique feature is that it is a decentralized digital currency that is not associated with any government or central bank. Bitcoin's underlying technology is blockchain, a distributed database that stores all transactions and keeps them secure.

Bitcoin can be used to carry out various financial transactions, such as transferring funds or purchasing goods and services from online stores. It has also become an investment target, attracting the attention of both professional traders and ordinary people. Bitcoin has a limited supply of 21 million coins, making it a valuable resource and also protecting against inflation.

However, Bitcoin has also come under criticism due to its volatility and possible use for illegal purposes due to the anonymity of transactions. Different countries have different legal approaches to regulating Bitcoin, from a complete ban to its legalization and regulation.

It should be noted that in addition to Bitcoin, there are many alternative cryptocurrencies called altcoins, each of which has its characteristics and advantages. However, Bitcoin remains the most popular and widely used cryptocurrency in the world.