Colonel is a high-ranking position in the ISA and Helghast militaries.

ISA

There is only one known Colonel, Jan Templar. However, unlike a typical army Colonel, Jan is seen performing the duties of both a navy captain, and a navy Admiral. 

Helghan Empire

Seemingly the opposite of the ISA, there are several known Colonels in the Helghan Army:

• Colonel Vyktor Kratek originally headed a Helghast refinery on Helghan and designed advanced weaponry. He was promoted to Colonel by Scolar Visari, and during the Helghast invasion of Vekta was ordered to seize the city of Diortem, and capture ISA Admiral Alex Grey.

• Colonel Mael Radec was Scolar Visari's personal bodyguard and one of the most fearsome soldiers in the entire Helghast Army. Radec lead several offensives against the invading ISA as well as the defense of Visari Palace.

• Colonel Tendon Cobar

Gallery

Presumably the ISA Colonel rank insignia, on Jan Templar's sleeve.

Presumably the Helghast Colonel equivalent.