According to the Memory Alpha wiki, it would be Geordi LaForge.

Geordi has held more ranks on screen than any other Star Trek character: he was an ensign in a flashback in TNG: "Identity Crisis", he was a lieutenant junior grade in TNG Season 1, a full lieutenant in TNG Season 2, a lieutenant commander in TNG Seasons 3 through 7 and the four Next Generation feature films, a commander in the illusory future of TNG: "Future Imperfect", and a captain in an alternate timeline in VOY: "Timeless".

That would be 6 ranks (Ensign, Lieutenant JG, Lieutenant, Lt. Commander, Commander and Captain), and includes all ranks with the exception of the flag ranks (Admiralty).

According to the Memory Alpha wiki, it would be Geordi LaForge.

Geordi has held more ranks on screen than any other Star Trek character: he was an ensign in a flashback in TNG: "Identity Crisis", he was a lieutenant junior grade in TNG Season 1, a full lieutenant in TNG Season 2, a lieutenant commander in TNG Seasons 3 through 7 and the four Next Generation feature films, a commander in the illusory future of TNG: "Future Imperfect", and a captain in an alternate timeline in VOY: "Timeless".

That would be 6 ranks (Ensign, Lieutenant JG, Lieutenant, Lt. Commander, Commander and Captain), and includes all ranks with the exception of the flag ranks (Admiralty).

According to the Memory Alpha wiki, it would be Geordia LaForge.

Geordi has held more ranks on screen than any other Star Trek character: he was an ensign in a flashback in TNG: "Identity Crisis", he was a lieutenant junior grade in TNG Season 1, a full lieutenant in TNG Season 2, a lieutenant commander in TNG Seasons 3 through 7 and the four Next Generation feature films, a commander in the illusory future of TNG: "Future Imperfect", and a captain in an alternate timeline in VOY: "Timeless".

That would be 6 ranks (Ensign, Lieutenant JG, Lieutenant, Lt. Commander, Commander and Captain), and includes all ranks with the exception of the flag ranks (Admiralty).

According to the Memory Alpha wiki, it would be Geordi LaForge.

Geordi has held more ranks on screen than any other Star Trek character: he was an ensign in a flashback in TNG: "Identity Crisis", he was a lieutenant junior grade in TNG Season 1, a full lieutenant in TNG Season 2, a lieutenant commander in TNG Seasons 3 through 7 and the four Next Generation feature films, a commander in the illusory future of TNG: "Future Imperfect", and a captain in an alternate timeline in VOY: "Timeless".

That would be 6 ranks (Ensign, Lieutenant JG, Lieutenant, Lt. Commander, Commander and Captain), and includes all ranks with the exception of the flag ranks (Admiralty).