A Colonel was a military rank of a commissioned officer. It is usually rated as the highest, or the second-highest field rank below a general.
Zachary Smith posed as a colonel to sabotage the Jupiter 2 mission. (The Reluctant Stowaway)
A second colonel, Colonel Mason, was mentioned by Will Robinson as being on Alpha Control's staff. (Return from Outer Space)
Jeremiah Smith claimed to be a colonel. (Curse of Cousin Smith)