Since the time of Karl Marx and Friedrich Engels, a variety of developments have been made in communist theory and attempts to build a communist society, leading to a variety of different communist ideologies. These span philosophical, social, political and economic ideologies and movements, and can be split into three broad categories Marxist-based ideologies, Leninist-based ideologies, and Non-Marxist ideologies, though influence between the different ideologies is found throughout and key theorists may be described as belonging to one or important to multiple ideologies.