What is a term for someone who plays the fool and is secretly not one?

Solution 1:

Such a person can be called a

Columbo

This comes from a US television program where the detective, Columbo, pretended to be well meaning but bumbling. Here's how you use it:

A helpful advocacy technique in special education meetings is to play Columbo and ask questions as though you didn't know the answer, for example, "Does IDEA allow the district to decide on its own to skip the triennial reevaluation?

Have you thought about using the Columbo approach?

Example I found on the internet:

Sometimes an attorney will pull a “Columbo” act and look like she is fumbling around trying to organize her notes or “thinking” of the next question when in reality, she is intentionally inserting a pregnant pause.