Then: Christopher Castile played the brainy fanny-pack wearing nerd Mark Foster on 'Step By Step.' He was also well known during that time period for his role as Newton family son Ted in 'Beethoven' and 'Beethoven's 2nd,' as well as providing the voice of Eugene Horowitz on the Nickelodeon series 'Hey Arnold.' All of these characters were (shocker!) also huge nerds. So what happened to him?

Now: Castile retired from acting when 'Step By Step' ended, and then proved to be every bit as intelligent as Mark Foster by getting a master degree and eventually becoming a highly rated political science professor at Biola University. The 31-year old also has a pilot's license, and, judging from the only current photo available of him, ended up doing far better with the ladies than his awkward TV counterpart.