Karl Adams is an agent with the CIA.
He is also, or very soon will be, an agent with the Russian SVR.
While there will be other changes in his life over time, those two facts are what make the majority of his adult life (so far) the most interesting.
Adams is the child of occasional CIA operative Jake Adams, a legendary operative with a large and impressive resume in the intelligence business and Toni Contardo, herself one of the Agency's most valuable and experienced field agents. Those two enjoyed a long term deep friendship dating back two decades, though it was one with sizeable gaps due to each having their individual missions to perform for the government. One of their earlier liaisons had resulted in Contardo getting pregnant and having Karl. For reasons never quite explained, she chose to keep the existence of Karl a secret from her lover Jake; he learned about Karl and his relationship only at the mother's funeral. Karl was a young Air Force Lieutenant by that time. Over the next few years, son and father would meet on numerous occasions and become close.
When we first meet him (in his own series) he is living in Murmansk under the alias of a Spanish citizen, Nicolas Lobo, a student in the university in that city becoming even more of an expert in the Russian language as he was when he first traveled there. He had no particular mission when in that first recorded adventure other than to immerse himself in the city and the school but that will change fairly quickly. So will his identities as he will shuck off that Spanish one to become Nikolai Krupin and then later Nikolai Markin; the legend makers at Langley doing excellent work as usual.
In time his identity will shift to being a more "permanent" Nikolai Ivanov as he makes the transition, under Agency orders, of course, to being a recruit for the SVR and eventually becoming one of its operatives. His life becomes quite complicated as he works to spy on the Russian intelligence operations for his American bosses even as his Russian employers find opportunities for him to travel to the States to spy on America for them!