Charlton Comics
Sarge first appeared in his own title, Sarge Steel #1 (Dec, 1964). His title would last until #8, at which point it was retitled Secret Agent, and cancelled with #10 (October, 1967). After that, his series continued in Judomaster #91-98 (the stories in #91-96 fit in the year-long hiatus between issues #9 & #10, as all his stories are listed as 'File #xxx'). Sarge also appeared in short spots on self-defense in Fightin' 5 #34 and 37 and in the Sentinels stories in Peter Cannon, Thunderbolt #57 and 58 as their CIA contact.
His enemies included characters like "The Lynx," "Ivan Crunch," "Smiling Skull" (a Nazi villain who fought Judomaster during World War II), Werner Von Wess, Mr. Ize, and others.
Sarge was originally a hardboiled private eye (in fact, in the book The Fine Art of Murder, Max Allan Collins notes that Steel was the first fictional private eye to be a Vietnam veteran), who somehow also got involved in "spy cases," and became by issue #6 a "Special Agent." The final issues were titled Secret Agent, even though Gold Key Comics also published a comic of the same title in 1967 based upon the television series, Danger Man.
Read more about this topic: Sarge Steel