Samuel "Sam" Vimes is the Commander of the Ankh-Morpork City Watch. He is the central character of the Watch Series, in which he rises from being a poor and often-drunk policeman to being the leader of a modern police force.
During his first appearance in Guards! Guards!, he is the Captain of the (useless) Night Watch. He is promoted to being the Commander of a reunified City Watch at the end of its sequel Men at Arms, and presides over the Watch's transformation into a modern police force. Through his detective work and adventures he saves the city and many people's lives on multiple occasions. He is often referred to as the second-most powerful man in the city after Lord Vetinari.