The Clocksmith was a renegade Time Lord and a member of the Doom Coalition. He was an artist who strived to create the best pieces of art in order to evoke a reaction from the universe and believed that nothing should stop his art from being made. He was obsessed to the point of madness with his work.
He worked with various mediums of art work, but he preferred working with metal, and even encased people in metals like lead or strontium.
He travelled in a Type 70 TARDIS and used a device to freeze people's molecules to capture the perfect pose for his artworks while subjecting them to terrific pain and manipulated their bodies to assume those poses in the first place. He also used this device to kill people. (AUDIO: The Doomsday Chronometer)
When the Eleven's TARDIS briefly materialised in 15th century Prague, it deposited some of the metal alloy from Syra's core, doused in temporal energies. The Clocksmith gathered this metal and for the Coalition, made the pieces for the Doomsday Chronometer. The Chronometer would supposedly mark the end of the universe. (AUDIO: The Eighth Piece)
At some point, the Clocksmith travelled to the Solvers' homeworld. There he created amusements for the Solvers and their Queen, Risolva. This was a deception to gain their trust. He then dismantled Risolva and took control of the Solvers, who he then took to 15th century Prague and England 1538 as his henchmen. Risolva reassembled herself and sought the Doctor's help in retrieving her people. This was successful, and the Solvers betrayed the Clocksmith. The Doctor instructed Risolva and her Solvers to scatter and protect the pieces of the Chronometer so that it would take a long time to be fully assembled.
The Clocksmith travelled along his Chronometer's timeline and saw that it would not be fully assembled until 2016. He created the Revelation Sect to find and assemble the pieces of the Doomsday Chronometer. In Rome 2016, the Clocksmith acquired the lost Eighth and Ninth pieces of the Chronometer from Helen Sinclair and River Song and assembled the Chronometer. By measuring doomsday, the Chronometer had caused it to happen.
After killing Octavian, whom had been stowing away in his TARDIS in order to warn others of the impending disaster, the Clocksmith was killed by Risolva's Sovlers, and his TARDIS was stolen by the Eighth Doctor and River Song. (AUDIO: The Doomsday Chronometer)