Complex sentence: His first appearance was in the episode originally broadcast on 10 January 2005, being introduced by executive producer Kate Harwood, and he has appeared in at least one episode every year until 2013, making his last appearance on 24 December 2013.
Split into simpler sentences: His first appearance was in the episode originally broadcast on 10 January 2005, being introduced by executive producer Kate Harwood, and he has appeared in at least one episode in every year since. However, didn't appear in 2014, making his last appearance on 24 December 2013.