Ghostwheel is a trump- and pattern-based computer constructed by Merlin in a Shadow where Earth physics do not apply. By Merlin's description Ghostwheel's operations involve "a lot of theoretical crap involving space and time and some notions of some guys named Everett and Wheeler". Ghostwheel speaks with Merlin's voice, occasionally causing confusion, and usually takes the appearance of a spinning circle of light. Ghostwheel usually addresses Merlin as "Dad."
After finishing construction, Merlin set Ghostwheel to work indexing Shadows in the same way that a search engine indexes the internet. Similar to a search engine, Ghostwheel can find, track, and retrieve objects from Shadow; this includes the ability to move people and objects between Shadows. Ghostwheel operates by creating pseudo-Trumps for every mutation of Shadow and then searching them.
Merlin designed Ghostwheel as a tool to be used by Random, King of Amber, for keeping watch on Shadow for the protection of Amber. When introduced to Ghostwheel and its abilities, Random was immediately struck by the construct's potentially dangerous power and ordered Merlin to deactivate his creation. However, by this time Ghostwheel had attained sentience and resisted shutdown.
After regaining Ghostwheel's trust, Merlin came to rely heavily on his powerful creation, and Ghostwheel features as a major subcharacter throughout Merlin's saga. By the conclusion of the series, Ghostwheel had developed enough that his support of Merlin forced the Pattern and the Logrus to treat the pair as nominal equals rather than pawns.