The Sentient Intelligence, or SI for short, is a planet-sized autonomous computer entity in the Commonwealth Saga books by Peter F. Hamilton. It was created by mankind at some point before the events described in the first book, Pandora's Star.
It generally stands off from the Commonwealth and tries not to get involved in the messes that humans get themselves into, although if it deems it necessary, it will intervene. It also has been known to act through a human agent (such as Mellanie), and uses smaller versions of itself to provide interim support when connection to the full SI is not possible. It is an expert in infiltrating systems undetected and controlling them covertly, although a skilled operator can sometimes sense its presence.
It is sometimes considered (in the books) that the SI is an “intellectual snob” – it considers itself above humans, but is nevertheless fascinated by them.
It is connected to the Commonwealth by a micro-width wormhole, but its exact location is unknown. The SI will communicate directly only with a select few people in the Commonwealth, such as Nigel Sheldon, who helped to create it. People can elect to have their memories and personalities stored in and incorporated into the SI. As such it is almost a collective mind, and refers to itself as “we”.
Non-sentient computer devices/programs in the Commonwealth Saga are called Restricted Intelligences or RIs and are sometimes designed by the SI.