Marvel's Ultimate comics had a knack for finding a unique angle on the publisher's most familiar characters. While the line started with the intention of simplifying and modernizing the continuity of the comics' mainstream 616 characters, it became infamous for some of its worst moments. It's also too-often dismissed as an overly "grimdark" depiction of Marvel's stable. Quite the contrary, there were highlights to the Ultimate 1610 continuity and no better example could be found than Ultimate Captain America. In fact, he might be the best Cap ever.
Much of the origin for the 1610 Captain America is quite the same as the 616. Whereas most other Marvel heroes needed their origins updated or tweaked a bit for the modern day, such as making the spider that bit Peter Parker the result of genetic tampering rather than radioactivity, when it came to old Steve Rogers there wasn't much need to change the nitty gritty details. He was a sickly Brooklyn teenager in WWII eager to fight for his country, transformed by the Super Soldier Serum into America's greatest defender, then preserved in ice until the modern day when he awoke.
What proves most interesting are not the similarities between the Ultimate Captain America and the one most fans may be more familiar with, but the differences. Ultimate Captain America was certainly still a noble hero eager to fight for his country and lead his fellow superheroes into battle with an inspirational speech -- the big difference is that he did all that while still being a flawed individual. His 1940s values preserved right along with his body, Ultimate Cap had conservative views on women's clothing and the use of swear words that weren't just little character details, but outright flaws that caused him problems.
Ultimate Captain America was far from perfect and has masculinist "take charge" attitude went from charming to outright grating throughout the course of his relationship with Janet van Dyne, the hero Wasp. Whereas Wasp enjoyed the old-fashioned attention and care Cap gave her following her abusive relationship with Henry Pym, Cap stepping to protect her and offhand judgement of her decisions proved annoying enough to drive a wedge between them. Even apart from his values at large, Steve just had a hard time connecting with those around him, as his entire world and interests became relics of the past.
The whole exploration treated the "man out of time" aspect to the character in a much more serious and realistic manner than the MCU's version. On film, Cap's WWII-era world views come across more as charming character traits that don't really run through to his core. His noble heroism is more a timeless trait any classic hero would have than him being the embodiment of an era since past. Similarly, the 616 version is practically a moral paragon of everything right and true in the world. It makes for great iconography, but just doesn't feel as three-dimensional.
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That's not to say Ultimate Captain America's appeal wasn't all heady seriousness and flaws. Especially in the later comics, as he grew and developed from his flaws to become more comfortable in the modern day, he became much more similar to his mainstream counterpart in leading America during its most divided times. During those moments, Marvel cranked the dial to 11 and made him a stupid amount of dumb fun, even becoming the President of the United States who never removed his costume while in office and punched the crooked politicians who disagreed with him.
Ultimate Captain America's growth from a realistic portrayal of a man out of time into over-the-top and action-packed catharsis comes as a genuinely interesting development of the character rarely seen elsewhere. Whether it's in the 616 or on film, it's rare to watch Cap develop as a character. He's always so fully formed, with other characters aspiring to be like him. There's nothing wrong with being iconic, but it can also be a bit boring. When it comes to enjoyable characters, it's the flaws that truly make them perfect -- and it's what makes Ultimate Captain America the ultimate Captain America.