Ronnie Soak is the fifth
Horseman of the
Apocalypse, making his appearance in
Terry Pratchett's 26th
Discworld novel
Thief of Time, published in 2001 by Corgi and Doubleday.
Ronnie left the Four Horsemen of the Apocalypse before the four other horsemen (Pestilence, Famine, War, and Death) became famous. His mythical name is Kaos and he was one of the first (super-)natural powers imagined by mankind.
In current days, Ronnie is happy running a dairy as a milkman, unless greater events force him to ride out with the four horsemen again. He is quite known for his milk products and his supernatural punctuality.