...was actually worn by the celebrity in real life by choice and not paid endorsement. Now we all know the 1133 Monaco is the "Steve McQueen" because he wore it in "Le Mans," but there is not much evidence that he wore the watch offscreen.
But here's a famous fellow with reknowned taste and style who was never paid to wear any watch and wore what he wanted while doing his rarified work...

The late Peter Jennings at his desk wearing his 1133 Heuer Monaco.
Cheers,
T.