A tactician is someone who is skilled in the planning and execution of military tactics.
Khan Noonien Singh called Captain James T. Kirk an "excellent tactician". (TOS: "Space Seed")
In 2365, an unnamed Ferengi served as tactician aboard the Kreechta. (TNG: "Peak Performance")
When Garak and Julian Bashir had breakfast, Garak said about Julius Caesar, "this man is supposed to be the leader of a great empire, a brilliant military tactician, and yet he can't see what's going on under his own nose." (DS9: "Improbable Cause")
When talking to General Martok, Worf compared Gowron with Martok and said that he was not half of the tactician Martok was as his military experience was limited. (DS9: "When It Rains...")