Whose spacecraft first measured the atmosphere of Venus directly from inside it?

Venera 4, launched by the Soviet Union, entered Venus’s atmosphere on 18 October 1967 and transmitted data during descent. It was the first spacecraft to make direct measurements inside another planet’s atmosphere. The probe revealed a very dense atmosphere dominated by carbon dioxide, with temperatures and pressures far higher than expected. Those results changed scientists’ understanding of Venus from an Earth-like world to an extreme greenhouse planet.