Sarge Steel is an agent in American Intelligence.
His employment with a couple of different agencies was a gradual one, as is often the case. He certainly did not start out to be an agent but life took him places and opportunities, or necessities, came about and he ended up one very experienced operative.
He started out his adult life as a soldier, joining into the U.S. Army in 1960 and quickly moving into the Special Forces. His position there must have been interesting since his first name is Sargent. That made it natural for the nickname of "Sarge" to be attached to him but all evidence points to Steel having immediately joined as an officer, not enlisted, and, with the conflict in Vietnam heating up quickly, he was soon enjoying the rank of Captain. So, he was officially Captain Sargent Steel.
No matter his name or rank, his training in the Service was intense and he learned a great many things about survival and combating the enemy, skills that would keep him alive in many a nasty scrape later in his life. One of his talents was noticed soon and his time in the military shifted from fighting the other side to hunting down those ostensibly on his own side who were profiting illegally from the war effort. When a large army operates large activities in a foreign land, large amounts of supplies and armaments are needed and invariably large amounts go missing. Steel's job and his successes came from tracking down those involved in the missing.
This made him very well known and very much disliked by the miscreants who were doing the stealing and they decided to get rid of him through the use of a grenade tossed into a window at a fancy party he was attending. He grabbed the object and heaved it back out the opening, saving many lives, but the explosion cost him his left hand. The Army offered him a prostetic but he decided to pass on the flesh-colored synthetic skinned ones and went with one in keeping with his name - a steel hand.
Back in the States in need of work, he started a detective business. The same skills he used to hunt down war profiteers he now used to track people for civilian clients. He was pretty good at it, enough so that a lot of those found or being sought would try again and again to eliminate him but Steel's skills with martial arts, his prowess with a gun, and his now pretty lethal left hook kept him alive.
Over a short time the type of clients he attracted became more and more in the meta-human category and his cases moved from tracking cheating spouses or embessling employees and became master criminals, mad scientists, and other nasties out for some pretty naughty schenanigans.
Eventually he would be offered a position with the CIA and then to other agencies such as the Central Bureau of Intelligence and the Department of Metahuman Affairs.
Note: in the comic world it is annoying common for new writers and authors to decide to take the character into totally different directions and rather than just have the person change jobs, they often "retcon" (retroactive continuity) the character, essentially saying that what happened before really didn't and this is his new true past. This happened to Sarge Steel. The above data is based on his original life story.