Some of you may have only just met John Walker after his debut as the new Captain America in The Falcon and WInter Soldier's first episode. Here in the comics world where he's from, he's grown into his own hero - the US Agent. But in a strange turn of events similar to Cap, US Agent has been replaced by a new US Agent.
The only thing constant is change, as they say.
Check it out in this preview of next week's US Agent #4:
US Agent #4 preview
TL:DR, in US Agent #1 - #3, John ran into his estranged sister Kate while on a mission in rural West Virginia. Kate, a former SHIELD agent, was found working with a mysterious soldier operating as a new US Agent - and as you can probably see a mile away, they have a beef with Walker, the original US Agent. It ended up with Walker being kicked out of a SHIELD helicarrier while thousands of feet in the air, leading to what you see in US Agent #4.
"Conflicting visions of America intersect in a small mining town where long-buried SHIELD secrets are unearthed, forcing a confrontation between John Walker and his own sister, who has commandeered powerful weaponry she is poised to unleash on the townsfolk Walker has sworn to protect," reads Marvel's synopsis for the issue.
Want to know more about John Walker? Read our guide to US Agent - in comics and in the MCU.