Vilfredo Pareto developed the Pareto principle

Welfare economics is a field of economics that looks at the problem of allocating resources. It uses techniques from microeconomics to assess general well-being. From this assessment, it tries to find an allocation of productive factors as to desirability and economic efficiency within an economy, often relative to competitive general equilibrium. It analyzes social welfare in terms of economic activities of the individuals that compose the theoretical society considered. Individuals and their economic activities are the basic units for aggregating to social welfare. The aggregation may focus on a group of people, a community, or a society. There is no "social welfare" apart from the "welfare" associated with its individual units.