Gangsters are members of organized crime - they come in several varieties but the most common subtypes are:

• Crime Lords (leaders of organized crime, who gain such power via being more ruthless and feared than any other gangster within their territory, a Crime Lord holds unquestioned power within their organization and is often at "war" with other Crime Lords, who threaten their position : Crime Lords often obtain so much power they can easily continue to run their empires even when imprisoned.)
• Drug Dealers (some gangs do not allow drug dealing and may even actively hunt them down as "unwanted" influences, on the other hand many other gangs are extremely active in dealing with drugs - the most powerful drug dealers are often known as Drug Barons and are just as powerful and feared as Crime Lords.)
• Pimps (gangsters who are active in the "trade" of prostitution - often male but some times female - pimps are responsible for collecting money from their prostitutes as well as keeping their clients "in check" by ensuring they pay up and treat the prostitutes well - clients who fail to pay or whom abuse the pimp's prostitutes are dealt with accordingly : despite this "protection" many pimps are also highly abusive towards their prostitutes themselves, to ensure they stay in the "business" and do not try and move onto another life (and cost the pimp money in the process).)
• Thugs (the more violent members of organized crime, who actively engage in acts of violence and often enjoy such acts - often used as "muscle" by other gangsters they may intimidate or harm others on behalf of their gang or crime-lord : some Thugs hold no real aim in life other than violence for sheer "fun", these are known as Hooligans and if they form gangs it is normally just for fighting and vandalism.)
• Prison Gangs (life in prison is ruled by gangs, many of which exist only within prison and offer protection to like-minded inmates while also actively warring with those of rival gangs - these types of gangsters are common in especially violent prisons but can occur anywhere large number of inmates may be kept for prolonged periods of time.)