Uno is an agent for the United Nations.
Technically he is Jim Blake, the U.N.'s "trouble-shooter".
As stated in the first recorded adventure: "When the United States beat the Axis into surrender and emerged victorious from the most colossal war in history, they formed the United Nations Organization (U.N.O.) to help keep the world peace. But knowing there would be problems whose solutions would require unusual tactics and handling, the Security Council of the U.N.O. has secretly hired famed trouble-shooter Jim Blake! Known only to a few members of the Security Council, Blake operates under the name of 'Uno' - the United Nations Trouble-shooter!"
So Blake assumes that codename and it is by that he is best known though he does not especially try to hid behind it. After that first adventure, it appears as though he has been busy because people seem to know him, as Uno, wherever he travels. Usually he is welcome by the powers that be because of his ability to help them out of trouble but sometimes there is hesitation, explained by him when he stated once "where I show my face it usually means trouble".
Uno is a hands-on kind of operative, though fist-on might be more accurate. He has no qualms about jumping into a fray and letting the bad guy have it with a left or a right. He, unfortunately for his skull, is on the receiving end of things as well.
Though we do not have a large number of adventures of Blake/Uno, those we do have show him in the company of beautiful women and showing appreciation for their presence which is reciprocated. One lady on the side of the bad guys, when Uno is revealed, commented "So that is the great Uno! Well, well -- he is a handsome dog, is he not?". Later he will run into an undercover female agent on his side who shows her happiness as seeing his having escaped a nasty trap by planting her lips squarely on him. Uno, being a 40s man of action, though, will chide her "Easy, honey! Don't let your enthusiasm run away with you! There no time for that now!" Later he encounters the bad side woman again and entreats her to "come over to my side, beautiful. I can do more for you". When asked what he could do, he is the one doing the lip-planting. Apparently it works because she switches sides with a "mmm -- it's had quite an effect." [Note to bad side ladies falling for Uno. It did not work out well for her though her dying request was for him to kiss her again. Must have been some kiss.]