Throughout their shared Marvel Comics history, Wolverine have always had an unspoken bond of two fellow soldiers who served together in World War II. This is true in at least two universes across the wider multiverse, and in one of those realities, Captain America has a nickname for Wolverine that turned their brotherly bond into a weapon.
On both Earth-616 and Earth-1610 (main universe and Ultimate Universe), Wolverine and Captain America both fought in World War II, and in both universes, they did so before Wolverine was subjected to Weapon X. In the main continuity, Wolverine is slowly able to his life before Weapon X, learning that his name is James Howlett, and recollecting some of the events of his life prior to his mind-wiping torture. In the Ultimate Universe, however, Wolverine never regains those memories and the blank spaces in his life drives him crazy. So, when Captain America comes along– someone who knew Wolverine before he lost his memory–Cap uses that to his advantage when the two find themselves on opposite sides of a battle.
In Ultimate War #4 by Mark Millar and Chris Bachalo, Magneto has declared war on humanity, and all of his crimes are being held over the X-Men’s heads as well just because they are somewhat d with him. In response, the Ultimates are called into action to take the X-Men in until the situation can be resolved, only the mutant militant group doesn’t go down without a fight. In this issue, Wolverine is face-to-face with Captain America, and by doing something as seemingly trivial as calling Wolverine by the nickname of "Jim," Cap gains a huge advantage over him.
Since Wolverine can’t his life before Weapon X in the Ultimate Universe but Captain America re Wolverine during their shared experience during World War II, Cap is one of the only people alive that could help Wolverine fill in at least some of the gaps missing from his past. However, in this instance, Captain America isn’t interested in helping Wolverine, so when he calls him "Jim" (a name that means nothing to Wolverine), he is just trying to get into Wolverine’s head and psych him out during their fight. This isn’t the only time this has happened during one of their fights as Captain America has also referred to Wolverine by his army nickname, "Lucky Jim." Wolverine got that nickname after inexplicably surviving a number of fatal injuries in the war. Fans know he survived because of his healing factor, but his fellow soldiers just thought he was lucky, hence the name. While that could have been a piece of Wolverine’s history shared by Captain America in friendship, it was instead used against him just so that Cap could beat him in a fight.
This trend speaks as much to Ultimate Captain America’s ruthlessness as it does to the tragedy of Wolverine’s character. On Earth-616, Captain America and Wolverine bonded over their experiences in World War II, but on Earth-1610, Captain America uses the unimaginable hardship endured by Wolverine as a tactical advantage. Captain America pokes Wolverine’s trauma just enough to get him to make a mistake by using a nickname Wolverine couldn’t but wished so hard that he could, effectively turning their bond into a weapon.
