Sometimes, people make mistakes using “that” when referring to specific persons. The general rule is that is used to refer to any persons and not a specific person. For example:
The people that go to the opera are usually well-educated.
This example refers to people in general so “that” is aceptable. You can use “who” instead of “that”. Both are correct.
The person who bought the Ferrari was a member of Podemos. Here the person is specific and “who” is correct.
As a general rule, it is better to use “who”, as “that” can be incorrect or odd (extraño) in some contexts.