Just to share an article from UbiBlog..
How Edward Kenway becomes an Assassin
A very interesting read for all Assassin's Creed fans and those looking to jump into the series. The article, while not revealing too much spoilers, talks about how the pirate Edward Kenway became an Assassin, and even how he became a pirate.
It also shows the differences between Edward and the other Assassins before him and how they perceive the Assassin's Creed. What being an Assassin means to each of them.
Oh and some AC3 Spoilers..
For me personally, I'm hoping to see some backstory of Haytham Kenway as well. In Assassin's Creed 3, it was pointed out that Haytham was an Assassin first before he became a Templar so I hope AC IV tells the story on what really happened that made him switch..