Marvel’s new TV show, Agent Carter, is set in 1946, a year before the Cold War really started. But that decades-long conflict was brewing as soon as World War II ended, and Peggy Carter and her colleagues in the SSR would have had an eye on Russia by the time the show begins.
In fact they may already have their eyes on Russia. The first two episodes of the series have established the threat that will face Peggy and Jarvis as they try to clear Howard Stark’s name: Leviathan. Sure, that was the name of the giant snake alien in the Battle of New York in The Avengers, but that name has also been used for a secret organization in the Marvel Universe: a spy group based out of - you guessed it - Russia.
If the Leviathan in Agent Carter is in fact based on the Leviathan from the comics there's only a loose connection. The group first appeared in Secret Warriors in 2010, and it was revealed that it had grown out of the remains of the Soviet structure, much as Hydra grew out of the remains of the Nazi regime. Leviathan’s thing was that they froze 10,000 of the USSR’s best operatives (using the same techniques with which The Winter Soldier was kept on ice) in an effort to create super soldiers using alien Brood genetics*. The group acted up during one of the occasional periods when SHIELD was disbanded, leading to a war between Leviathan, Hydra and Nick Fury, who had assembled a new team of Howling Commandos.
You can probably already see where my thinking is going on this. If Leviathan is a Russian secret organization in Agent Carter, might they not be the people who turned Bucky into The Winter Soldier? Captain America: The Winter Soldier left large elements of the character’s transformation up in the air, including why he has that red star on his arm. That doesn’t make a lot of sense if Hydra created him, but if - as in the comics - it was the Russians it works better.
Leviathan makes a lot of sense as the group that turns Bucky Barnes into the Winter Soldier, which is very possibly happening concurrent with the events of Agent Carter. Perhaps there’s even a piece of stolen Stark tech that will create The Winter Soldier’s bionic arm, or the process that keeps him in suspended animation (known as Cold Storage in the comics).
Even if Marvel wanted to have Leviathan create and operate The Winter Soldier in Agent Carter, would Sebastian Stan appear on the show? Here’s where it gets interesting; while Agents of SHIELD is wholly run by Marvel TV, Agent Carter operates under the auspices of Marvel Studios. Kevin Feige is heavily involved, and Louis D’Esposito, co-president of Marvel Studios, directed the pilot. Joe Russo, half the directing team of Captain America: The Winter Soldier, directed the second episode. Stan is signed to a nine picture deal with Marvel Studios - could they tweak that to have him appear here? Or is Stan just enough of a team player that he’s willing to show up outside of his contract?
I don’t have any inside info on this, and I’ve avoided hitting up my sources because I just love this speculation game, but I have to imagine the name Leviathan was chosen purposefully. While Marvel TV and Marvel Studios don’t work completely hand in hand, they’re close enough, and Agents of SHIELD season two has been heavily influenced by Secret Warriors - the same comic that introduced Leviathan. With all those Secret Warriors comics influencing one Marvel TV show, could they have influenced another? And now that I think about it, could Leviathan burst from Agent Carter and show up in Agents of SHIELD? Let’s assume Leviathan does create The Winter Soldier - at some point he ends up in the care of SHIELD/Hydra. Could that be the longer story of Agent Carter, of the eventual capture of the Winter Soldier and crushing of Leviathan… which then returns in the modern day when SHIELD and Hydra both seem to be defeated, leaving the field open for the secret organization to rise again? This could lead to an Agents of SHIELD arc that essentially adapts the storyline where Leviathan first appeared. Imagine a three way spy war between Leviathan, Hydra and Coulson's underground SHIELD.
It all seems too complicated and unlikely… but this is Marvel we’re talking about.
* Fox likely owns the Brood, who are probably part of the X-Men package, but there are plenty of other alien lifeforms available. After all, SHIELD has had a Kree on ice for who knows how long, and they were definitely experimenting with its genetics.