Mariner 10 launched 1973

Mariner 10, launched November 3, 1973, was the first spacecraft to to visit two planets.  It was the last spacecraft of the Mariner program.  It made a flyby of Venus in February 1974.  It proceeded to make three flybys of Mercury in March 1974, September 1974 and then March 1975.  

Mariner 10 was decommissioned shortly after.