William Shepphard first patented liquid soap on August 22, 1865. In 1980, the Minnetonka Corporation introduced the first modern liquid soap called SOFT SOAP brand liquid soap. Minnetonka cornered the liquid soap market by buying up the entire supply of the plastic pumps needed for the liquid soap dispensers. In 1987, the Colgate Company acquired the liquid soap business from Minnetonka. http://inventors.about.com/library/inventors/blsoap.htm

The soap as we know it today (solid as well as liquid) was invented by Muslims in the beginning of 7th century, the same exact formula is being used today. From wiki page for soap: True soaps made from vegetable oils (such as olive oil), aromatic oils (such as thyme oil) and lye (al-Soda al-Kawia) were first produced by Muslim chemists in the medieval Islamic world. The formula for soap used since then hasn't changed. From the beginning of the 7th century, soap was produced in Nablus (West Bank, Palestine), Kufa (Iraq) and Basra (Iraq). Soaps, as we know them today, are descendants of historical Arabian Soaps. Arabian Soap was perfumed and colored, some of the soaps were liquid and others were solid. They also had special soap for shaving. It was sold for 3 Dirhams (0.3 Dinars) a piece in 981 AD. The Persian chemist Al-Razi wrote a manuscript on recipes for true soap. A recently discovered manuscript from the 13th century details more recipes for soap making; e.g. take some sesame oil, a sprinkle of potash, alkali and some lime, mix them all together and boil. When cooked, they are poured into molds and left to set, leaving hard soap.

People have been using liquid soap almost as long or as long as there has been soap. soft liquid soaps were very common in the Middle east hundred of years ago.

Some dude who did hard time in prison.