The influential philosopher known for their theories on morality and ethics is Peter Singer. A leading figure in applied ethics, Singer's work focuses on practical ethics concerning issues like animal rights and global poverty. His book "Animal Liberation" argues against speciesism and advocates for the humane treatment of animals. Singer promotes a utilitarian framework, encouraging individuals to consider the consequences of their actions on others. His ideas have profoundly impacted philosophical debates on ethics and social responsibility, making him a pivotal figure in contemporary moral philosophy.