commander-in-chief; supreme commander
Military or historical use; refers to the highest-ranking officer in command.
He was appointed commander-in-chief of the allied forces.
Common in sports and club activities; the leader of a team.
He is the captain of the soccer club.
He serves as captain of the soccer club.
Our army struck down the enemy commander.
The team chose her as captain.
The newly joined player was appointed captain.
司令官 refers specifically to a military commanding officer, whereas 主将 can mean either a military commander-in-chief or, more commonly today, a sports team captain.
部員 refers to an ordinary club/team member, in contrast to 主将, who is the team's leader or captain.
大将 is a specific military rank (general/admiral) or a casual term for a boss, while 主将 means the person in command or acting as team captain, not a fixed rank.
From 主 (master, chief) and 将 (general, leader). The compound originally referred to a military commander-in-chief and later extended to sports team captains.