Poindexter is a recurring character in which American TV cartoon series?

Felix the Cat (originally called Master Tom) is a cartoon character from the silent film era, being the first cartoon character in history to win a high level of popularity.

Poindexter, who also sometimes goes by the nickname "Poinsy", is a genius scientist who is both the Professor's nephew and a friend of Felix. Basically, still being a child, Poindexter falls under the "minion with an F in Evil" topic, though his IQ level (which is either 222 or 777, depending on sources) gives him A's in everything else, especially science. The button on his shirt allows him to temporarily glitch machinery as seen when it stopped Master Cylinder from attacking him and Felix.

Although who and where his parents are (or if they're even still alive) is still unknown, Poindexter is the apparent pride-and-joy of his uncle, the Professor.

Poindexter's signature appearance is in "Felix Babysits" when Felix takes a job to babysit for the Professor for the night (mostly out of surprise and curiosity of how the professor could even have a baby), and Poindexter comes to his uncle's calling... but not before an explosion from another rocket-fuel failure, and when he got a scolding reminder that the lab's off-limits, Poindexter jokes "There's no fuel like an old fuel" (Felix sarcastically called the boy a "funny man"), and when they shake hands for the first time, Poindexter plays a practical-joke on Felix using a joy-buzzer, and then uses the model of his new force-field.