When Gilligan left much of Walter 's past unexplained during the development of the series , the actor wrote his own back story for the character .
Cranston contributed a great deal to the character 's persona .
When Gilligan left much of Walter 's past unexplained during the development of the series , the actor wrote Cranston 's own back story for the character .
Cranston contributed a great deal to the character 's persona .