The Five Kingdom classification system was proposed by Robert Whittaker in 1969 and is used to categorize all living organisms into five main groups based on their unique characteristics:

1. Monera: This kingdom consists of prokaryotic organisms, such as bacteria, that have simple structures and lack a nucleus and other membrane-bound organelles.
2. Protista: This kingdom includes single-celled eukaryotic organisms, such as algae and protozoa, that have complex structures and a nucleus and other membrane-bound organelles.
3. Fungi: This kingdom includes multicellular organisms, such as mushrooms and yeasts, that are heterotrophic and obtain their food by absorbing nutrients from other organisms.
4. Plantae: This kingdom includes multicellular organisms, such as mosses, ferns, and flowering plants, that are autotrophic and make their own food through photosynthesis.
5. Animalia: This kingdom includes multicellular organisms, such as mammals, birds, and insects, that are heterotrophic and obtain their food by ingesting other organisms.

This classification system provides a framework for understanding the relationships between different groups of organisms and helps in the study of biodiversity.