Mathematicians who started out studying something else

I did not know much about modern mathematicians's biographies. One of my friend has just told me Edward Witten was a history student when he was undergradute. Are there any different modern mathematicians who were not a mathematics(physics?) student, and then they changed their mind to be come a mathematician(physicist?)? We have already knew that Gauss was also interested in philosophy in the past, but he changed after proving the cosntrucible of Heptadecagon.

In fact, I did search for the appropriate tag for this question, but I only found history is good enough. If you are a moderator, please help me. This is also a soft question, so please give me some example before closing it.

Thanks for reading.

This MO question has many examples of mathematicians who did this.