Economically--he has become the face of supply-side economics or "trickle down" economics. This policy believes in tax cuts to create job stimulus.
Politically--Reagan consolidated the conservatives and created the New Right coalition with libertarian economics, hard-line foreign policy, and religious conservatism.
Foreign policy--Reagan is often given credit for ending the Cold War through his speeches and meetings with Gorbachev. It can be argued Gorbachev is more responsible for the end as he refused to respond to Reagan's military increase and wanted to end the arms race.