Descartes was French, but he died in Sweden in 1650. Fans from his native country went to Sweden in 1666 and moved his body back to France. Along the way a bone and a finger were taken as souvenirs, and his head disappeared.
It turned up a couple of hundred years later and eventually ended up on display at the Musée l’Homme in Paris. At least they think it’s his head.
When the museum closed for renovation, the question came up about what to do with the great thinker’s skull. Some want it reunited with (most of) his body, in a church in Paris. Others want it sent to the Prytanée, a school in western France he attended as a young man.
Here’s a photo of the skull they think belonged to Descartes.
Skull’s Odyssey Tracked has more details.
And this article from January has details of the politics behind who gets to keep the skull.