Sierra, or Sierra-Online, is the gaming company behind the original AGI based games. It was founded in 1979, by Ken & Roberta Williams after their success with one of the first graphical adventures made, called Mystery House.
Between 1996 and 1999, several corporate shakeups involved Ken Williams leaving Sierra, and the closure of several departments of the company, including the Oakhurst Studio(Yosemite Entertainment), where adventure games were produced.
Today, Sierra is no more. It was renamed Sierra Entertainment in 2002. In 2008 it's ownership was transferred over to Activision and later on in the same year, Sierra was closed down for possible future sale.