The Spy Fighter is an agent with the S.I.D.
50 plus years in future from when the tales were first presented, we are introduced to the impossibly perfect man that is Saber, the Spy Fighter with these words:
"The year is 1997 ... Only three nations have emerged from the Great War of 1939 ... Russmany, ruler of all Europe and all Africa ... Mongo, the kingdom holding Asia and the Orient ... and Greater America, last refuge of democratic government, a powerful and rich nation, which includes both the continents of North and South America, and numerous islands in the Pacific."
Wouldn't you know it? Both Russmany and Mongo have temporarily banded together to take on and destroy their enemy but to do that, they decide they must "undermine her government with propaganda and spies". In desperation, America's Super Intelligence Department, hence the S.I.D., which was "created to combat this menace" went on the hunt for "a man who possesses both physical and mental ability of an unusual degree".
They found that man in Saber, "holder of all modern athletic records, and possessor of the greatest mind of our time ... combined with an almost supernatural knowledge of the art of telepathy". [It struck me odd that this man needed to be introduced to the group. Seems someone with such amazing abilities and accomplishments would have been known already to, well, everyone. Also telepathy is considered "almost supernatural" and is an "art".]
After Saber single-handedly routs the invading forces of Mongo, the President of Greater America appoints him as the "permanent" head of the S.I.D. As the head, he will still be the one he calls upon to repeatedly go it alone to fight all the enemies of the nation.
Speaking of enemies, in the opening of the series we are told there were two other nations on the planet but in the second adventure we meet a third called Antartica. For several adventures thereafter, we learn of schemes and attack by "a foreign power". One of these speak German and is named Prussania. And then there is Grontonia. And so forth. A good number of countries, each with a desire and a plan to destroy Greater America (abbreviated U.S.) but always Saber is there to stop them.
Saber starts out having the best mind and body with telepathy as a plus. He will go on to gain additional prowess here and there, such as the strength to hurl heavy objects several miles away. That not being enough, he attains "a power of voluntary growth", having now the ability to enlarge to near planet shape (he was floating in space at the time where apparently he did not need air). Saber does not have the power to fly on his own but he does have the magno-beams which he can ride through the air on. Not sure how they work or how they help him go from A to B but he gets there pretty fast.
Some of the more interesting ways the stories announce Saber are:
"The mightiest and most intelligent man in the world"
"The invincible defender of freedom"
"Possesser of the keenest intelligence in the world"
"The mighty man with the piercing brain!"
On the 14th adventure, everything switches for Saber and the world he inhabits. Instead of futuristic locales with spaceships and flying suits and ray guns and destructo-beams, not to mention Saber wearing a skin-tight red onesie, the time-frame jumps back to the early 1940s. Nazis are the enemies. Saber wears a three-piece white suit, unless he dons a disguise or a kafir. His abilities of telepathy and other exotic skills are no longer mentioned let alone used.
The last three adventures all take place in the Middle East with Saber, now apparently in British Intelligence, helping to stop the Third Reich. Maybe this Saber was an ancestor.