The relationship of Monkey D. Luffy, captain of the Straw Hat Pirates, and Edward Newgate, better known to all of One Piece's world as Whitebeard, serves as a cathartic core to Eiichiro Oda's sprawling universe.
The War of the Best: A Fateful Encounter
Well, it is in the Marine Ford Arc where Luffy scored the first and only face-to-face meeting with Whitebeard, which really becomes a cornerstone in the annals of One Piece history. For the reason that Luffy indulged in breaking through the great prison of Impel Down to save Portgas D. Ace, who was caught by the Marines, while he is also one of the commanders under Whitebeard, this incited the great battle. War and chaos let these two strong heads really meet face to face in order to open a door of complex acquaintance.
First, Whitebeard was suspicious about Luffy's skills and motives but was able to identify the enthusiasm and power of the young pirate. Upon realizing that the pirate was Luffy, Whitebeard went ahead and offered protection to the pirate in the middle of their fight. This was accompanied by adverse consequences.
Shared Traits and Ideals
Though the difference in age and experience between Luffy and Whitebeard is so great that their number of similarities found are very few, all in all both of them, without a doubt, are established, physically, through their strong determination and charismatic leadership.
Whitebeard's well-known pronouncement that he viewed all of his crew members as his "sons" resonates deeply with the essential nature of the Straw Hat crew as a family to Luffy. This aspect of the familial approach to being a pirate clearly demarcates these two captains from most of their peers and works toward establishing their legendary reputations.
The Spirit of D: A Common Thread
One of the most intriguing truths regarding the connection of Luffy and Whitebeard has to be the identification by Whitebeard of the "Will of D" inside Luffy. In the world of One Piece, the "D" in the name Monkey D. Luffy holds great significance and generally points towards those with high potential to change history.
Whitebeard had been Captain of the Moby Dick over which Gol D. Roger, the former Pirate King, sailed during his time. This, therefore, put Whitebeard into a better place to see, in Luffy, the same indomitable spirit that characterized Roger. It is this, most likely, that this one reason why Whitebeard agreed to protect Luffy during the Marineford War.
Inherited Legacies
While the personal interaction between them was rather brief, the effect Whitebeard made on Luffy's journey was huge. After his death and the battle at Marineford, many soldiers of his territories and soldiers that were his allies came to appreciate and now support Luffy as a worthy inheritor to the philosophy of Whitebeard.
This unofficial inheritance extends beyond territory. By all that he has done, Luffy has, even though unwittingly, started himself on the path that Whitebeard also walked—a path through the annals of history as a great destabilizer against the World Government.
The Ace Connection
This established quite a complicated relationship between Luffy and Whitebeard. Being one of Luffy's brothers and one of Whitebeard's subordinates places Ace in a position where he was the only connection between two greater powers. If ever there was a closer resemblance of Luffy's own capacity to fight the world, Whitebeard's readiness to make war to save Ace only points up the further extent of the depth to loyalty and family-like ties which the crew values.
Whitebeard's Foresight
An interesting theory among One Piece fans is that Whitebeard may have had some forethought about who Luffy will become or what the future of One Piece will be about, to some degree at least. Some interpret it as Whitebeard realizing at the last moment, in hindsight, that Luffy and not Ace would take over the will from Roger—maybe becoming the next Pirate King. That theory there just adds the full scope to everything that Whitebeard did in the War of Marineford.