Spymaster is one of Tony's best supervillains

I really believe he is a great foe to Iron Man and has proven to be very consistant one in that, and that's for a mantle that has been taken by three different people.
The original Spymaster is a classic rogue who managed to do some real harm to Iron Man in his trajectory, although he faked his death for a while. Now, apparently he's dead for real, but before that he managed to be the leader of various Iron Man villains in an operation to savotage Stark, which I think is a great role for him.
Iron Man's minor villains are often classified as just minions or goons, and Spymaster falls into that category, but being the leader of the underdogs is great for him.
Nathan Lemon, the weakest of the three, managed to lead his elite to give Tony the beatdown of a lifetime, since he was unarmored. He was also trained by Taskmaster which is so cool.
And finally Sinclair Abbot, who debuted around the Civil War era and was a great modernization of the concept, and being a genuine threat for Tony. His biggest feat is probably killing Happy, and since he hasn't recovered from that yet, it's probably fair to consider that a big achievement. He's also believed to be the one who showed up in Cantwell's run but I'm not really sure if that's intended to be him or the original.

I believe Spymaster isn't used much, especially in adaptations, because some find his name, concept or even costume to be outdated and silly, to which I clearly dissagre. Also, some don't use him because he fills the same role as Ghost in some stories and he/she has a more interesting set of skills and design. I also disagree with this take since the similarities between the two begin and end with corporate espionage, being totally different characters outside of that.

So, that's my ramble about Spymaster. Hope you appreciate him more and pray that he gains more relevance one day.