Who came up with of a pendulum clock

Rene Descartes
Galileo Galilei

Neither René Descartes nor Galileo Galilei invented the pendulum clock. The credit for inventing the pendulum clock goes to dutch astronomer and mathematician Christiaan Huygens. Huygens developed the concept of using a pendulum as a timing mechanism for clocks in the 17th century.

Pick one

Christiaan Huygens