A strategist was a sort of an advisor who planned strategic moves.
Admiral Mark Jameson called Mordan IV Governor Karnas a "dogged strategist". (TNG: "Too Short a Season")
In 2353, Kyle Riker was working as a civilian strategist advising Starfleet in its conflict with the Tholians. In 2365 he came aboard the USS Enterprise-D as a strategic attaché. (TNG: "The Icarus Factor")
Sirna Kolrami was a Zakdorn master strategist. (TNG: "Peak Performance")
According to Ma'Bor Jetrel, the Talaxian military strategists ignored a calls for a demonstration test of the Metreon cascade and initiated it on the moon of Rinax causing the death of 300,000 Talaxians. (VOY: "Jetrel")
Neelix called himself a "guide, strategist, explorer, and adventurer." (VOY: "Initiations")
The Alpha Hirogen Karr was well known as a formidable military strategist, notorious for his cruelty when participating in a holographic program aboard the USS Voyager. (VOY: "The Killing Game")