Which branch has the power to override a veto from the president?

The Legislative branch (US House and Senate) has the power to override a presidential veto. However, in order to do so, they must have a 2/3 majority (instead of the simple majority to pass the bill the first time) in order to do so. If they override the presidential veto, the said legislation becomes a law just as if the President was to sign the bill. Examples of places where this occurred:
1) Medicare Improvements for Patients and Providers Act (override vote House 383-41, Senate 70-26)
2) 2007 US Farm Bill (override vote House 317-109, Senate 80-14)
3) 2007 US Farm Bill (override vote House 316-108, Senate 82-13; clerical error repealed legislation)
4) Water Resources Development Act of 2007 (override vote House 361-54, Senate 79-14)
5) Private Securites Litigation Reform Act of 1995 (override vote House 319-100, Senate 68-30)