Gangsters, also known as mobsters, are criminals that participate in gangs or gang related activities. Some gangs are very loosely organized, but others are highly organized and efficient. They are recognized by federal governments as crime syndicates. Some well known gangs are the Yakuza, Hells Angels, and the Mafia. Keep in mind, Answers.com does not support questions about how to commit illegal activities, such as how to join a gang.