Penny is a fictional character on the American CBS sitcom The Big Bang Theory, portrayed by actress Kaley Cuoco. She is the primary female character in the series, befriending her across-the-hall neighbors Leonard Hofstadter (Johnny Galecki) and Sheldon Cooper (Jim Parsons), two physicists who work at the nearby California Institute of Technology (Caltech). Penny's lack of advanced education, but outgoing personality and social aptitude drastically contrasts with the personalities of the primary male characters in the series, even though she is considered part of their group. She is the love interest of Leonard, with whom she maintains a brief romantic relationship during the third season, which is later resumed in the fifth season and culminates in an engagement at the end of the seventh season and their wedding at the start of season 9. Penny is the only main character of the show whose last name was not revealed, although she has been occasionally referred to or addressed with the last name Hofstadter since her wedding.