Sergeant Frederick Colon has been a member of the City Watch for nearly thirty years. He is aged around sixty, and had been intending to retire to the country, but never really got round to it. He has probably been in the Watch longer than anyone else; he is also the only one to never really adapt to its changing nature, and often thinks of the days when it was just him, Nobby and Captain Vimes. It is reasonable to suspect that he was also the Sergeant mentioned in The Colour of Magic.