Aristotle - ancient Greece. Said animals are below humans because only humans can reason; therefore, we can use animals without consideration we’d give to people.
Aquinas - medieval. Said animals cannot reason; therefore, people can use them as they wish. His thinking became Catholic doctrine.
Descartes - renaissance. Said animals are automata and only humans have minds and souls; therefore only humans deserve compassion.
Animals cannot argue back, so had to put up with this.