Craig Stirling, Richard Barrett, and Sharron Macready are the Champions.
I cannot say for certain, though I suspect not, that they ever used that title for themselves nor did anyone else. The term comes from the phrase about them that they were the "Champions of law, order and justice" so in the case of these three individuals, it is meant that they "fought for a cause", not that they came in first, although considering that they routinely won, it would not have been inaccurate.
The three worked for Nemesis, a department inside the United Nations described both as an intelligence agency, and it certainly did its share of that all over the world, and as a law enforcement organization, which it also functioned as though exactly whose "laws" it enforced is arguable. It existed mainly to keep the peace and to save lives. It was run by an old hand at the spy business, W.L. Tremayne. While we do not learn a lot about this man in his 60s, it is obvious from his demeanor that he has been around for quite a while and seen just about everything. He can be irascible and demanding but he definitely cares about his people as much as he does the mission.
As the the Champions - Stirling, an American, and Barrett, British, were agents with Nemesis for some time prior to their first recorded adventure. Both men were single and dedicated to their profession. Macready, also British, was a highly regarded scientist and doctor, recently widowed, who was asked to accompany the two men on that mission because of her vital knowledge in biological experimentation.
That mission was to break into a highly secret Chinese research facility and get evidence of that communist country's work in the creation of a biological weapon. They were successful in getting it and getting the data and getting out again. Getting completely away, though, not so much. Rifle fire would severely damage their getaway plane and despite the piloting skills shown by Stirling, it came down in the rugged Himalayas. All three were badly hurt. And that is when they were changed.
Their damaged bodies were found an ancient and hidden civilization in those remote mountains and they were healed with the advanced technology the people possessed. For reasons not quite explained, though, the three were also given enhanced abilities which they would be able to use repeatedly in their subsequent work for Nemesis.
Telepathy, at least between the three, was a key gift and would allow them to communicate silently despite distances. Limited precognition was another ability that would let them get a glimpse of what was about to happen or what was currently happening elsewhere. Their mental and physical prowess were greatly advanced. And their five senses were highly strengthened.
At the request of the leader of the civilization that gave them these abilities, they agree to keep their gifts secret. No one else would be told of their powers, not even their boss Tremayne. In the case of that man, though, he might not have been informed of them but after a very short while and some improbable successes, it was plain that he suspected something and was wise enough not to ask questions and to just reap the rewards.