Please Explain who the Ultimate Nick Fury is

No, Ennis' Fury was a rascist and misogynist. It was yet another gratuitous Ennis book. I understand his point was to show how degenerative the world of the CIA is, but Fury was far more entertaining as a blue collar soldier turned James Bond.

Ennis' Fury would have been fragged when he was a sergeant.

Back to the original point. The classic Nick fury was first introduced as Sgt. Nick Fury, of the US Army Rangers in WW2, leading the Howling Commandos. He later appeared in issue 21 of the Fantastic Four, set in the present day, as a colonel, attached to the CIA. This utlimately led to Nick Fury: Agent of SHIELD, in Strange Tales #135, with Fury becoming the leader of the espionage and law enforcement agency (inspired by The Man From UNCLE and James Bond). This interpretation of Fury carried on through the years, but created a problem. When shown in FF 21, he was in his early 40's. As time wore on, his age became an issue; so, the Infinity Formula was created. It's a serum that Fury takes to keep himself young, but if he doesn't take it he will quickly die. Originally, Fury was portrayed as a superspy, but later writers made him more cynical and manipulative to fit the post-Vietnam and Watergate era (especially after revelations of questionable CIA operations).

When the Ultimate line was begun, a new African American version of Fury was introduced, based visually on Samuel L. Jackson. This Fury was a general and tied to the Gulf War, though it was later revealed that he was around in WW2 and was an early test subject of the Super Soldier Formula that gave Captain America his abilities.

The classic version was the basis for the Hasselhoff movie, though it was based on continuity from the late 80's/early 90's Nick Fury series, not the classic series with Jack Kirby and Jim Steranko. Starting with Iron Man, Samuel L. Jackson portrayed the Ultimate version of Nick Fury, since he was the visual basis and a comic fan. The current crop of movies tend to use more of the Ultimate interpretations of the characters (in varying degrees), so this made sense. Fury should factor heavily in the Avengers movie.