Charles Barry was hired in 1844 to rebuild the Houses of Parliament, which had burned down ten years earlier. It was decided the new building should include a clock tower and Barry enlisted the reputable clockmaker Lewis Vulliamy for the clock itself.
Big Ben is the name commonly used for the entire clock tower, but it was originally the nickname for the largest bell in the tower. The clock tower is now officially known as the Elizabeth Tower, after Queen Elizabeth II. Because reasons.
The origin of the nickname "Big Ben" has been boiled down to two theories: the first is that it derives from Sir Benjamin Hall, the portly Commissioner of Works. The other theory is that the nickname comes from the world of boxing. Heavyweight fighters of the time were sometimes called "Big Bens," after the heavyweight boxing champion Benjamin Caunt.
Each clock dial is engraved at its base. The engraving reads, in Latin, "O Lord, keep safe our Queen Victoria the First."