“Sesame Street” has introduced the children of the world to a number of neighbors over the years, from Oscar the Grouch to Linda, the deaf librarian, to Maria and Louis, who spoke English and Spanish with equal proficiency. But what viewers may not realize is that “Sesame Street” also introduced them to an undocumented immigrant. His name was Carlo, on both the show, and in real life. Carlo the character was a teenager who worked in Mr. Hooper’s store for five seasons. Carlo the actor is really Carlo Alban, who was born in Ecuador and arrived in the U.S. when he was eight. Alban discusses his off-Broadway play, “Intringulis,” which tells his personal story of fear, patriotism, and celebrity.