Wiktionary
n. Someone who provides significant impetus or guidance in a given venture, movement, enterprise etc.
Wikipedia
"Moving Spirit" is a science fiction short story by Arthur C. Clarke, first published in 1957. The story within a comic story is narrated by Harry Purvis, who is called to assist a scientist relative of his in a trial. The scientist has been brought before the court on charges of illegally brewing liquor. Purvis manages to get him acquitted, by arguing that he was actually working on a fictional "osmotic bomb." Purvis demonstrates this bomb by exploding it in the courtroom, thus "accidentally" destroying all the evidence. However, the scientist is later booked for driving under the influence.
The piece is one of two original stories written for Clarke's collection Tales from the White Hart, the other being " The Defenestration of Ermintrude Inch." Galaxy reviewer Floyd C. Gale praised the collection as "as light and frothy a conglomeration of sidesplitters as it has been my good fortune to read."
Usage examples of "moving spirit".
Only two things about the men were known for certain-that it was Heissman, who had a dozen prewar screenplays to his credit, who was the moving spirit behind this venture to the Arctic and that Gerran had taken him into full partnership in his company, Olympus Productions.
That bull had been the moving spirit of the herd, a figure rather of mythic than of material dimension.
Britain, as the largest carrier of seaborne trade with the greatest interest in the free flow of neutral commerce, was host nation, and Sir Edward Grey the moving spirit and sponsor, though not a delegate.
The Pure Soul is identified with the Moving Spirit which informs it, reflecting it truly with perfect understanding.
Themistocles was the moving spirit behind the Athenian-led Greek victory over the Persians in 480 b.