Captain America Returns

According to an article over on Yahoo (story), Steve Rogers' old sidekick Bucky Barnes took on the mantle (or bullet-proof shield in this case) of Captain America. While Bucky never swallowed the Super Soldier Serum back in 1940s (or at least he won't admit to the deed), he's donning a newly-designed suit, carrying firearms and bulked up while becoming a master of special operations (meaning he joined the Marines). Here's a bit more:

You can catch the Official Word from Marvel here.

Actually Bucky has been a running character in the Cap comic for several years. When they relaunched Captain America a few years ago one of the first stories was the reveal that the Winter Soldier was Bucky.

Also the comic where Bucky was killed never actually existed in a first iteration. Bucky's death and involvement was retconned in later years.

It's even been hinted at that the Winter Soldier was involved in Wolverine's original escape from the Weapon X facility. Marvel just loves complicating their own continuity.