Quote 1
Danglars nodded to show he was satisfied. In the eyes of the world, and even in those of his servants, Danglars played the indulgent father and good-natured fellow; this was one side of the part he had chosen for himself in the popular comedy he was playing: an appearance he had taken on, which seemed to suit him as it suited the right profile of one of those masks worn by the fathers of the theatre in Antiquity to have the lips turned upwards and smiling, while on the left side the lips were turned down and sorrowful. We might add that, in his family circle, the smiling, up-turned lips dropped and become down-turned and dismal ones, so that most of the time the good-natured fellow vanished, giving way to a brutal husband and tyrannical father. (95.9)
Here's a more common kind of transformation. In the same way as you might have an indoor voice and an outdoor voice, Danglars essentially has an indoor personality and an outdoor personality.
"Indeed," said Danglars, casting a sidelong glance at Dantès with a flash of hatred in his eyes. "Yes indeed, he is young and full of self-confidence. The captain was hardly dead before he had taken command without asking anyone, and made us lose a day and a half on the island of Elba, instead of returning directly to Marseille. (1.30)
Here we see a conflict of ambitions. Danglars wants what Edmond has worked hard to earn. This small-scale conflict of interest leads to, well, everything.
Quote 3
"I increased our wealth, which continued to grow for more than fifteen years, until the moment when these unknown catastrophes, which I am still unable to comprehend, arrived to seize it and cast it down—without my being to blame, I might say, for any of it." (106.38)
Danglars takes credit for all the increase, but is unable to own up to his failures. That's how it seems to go when dreams are destroyed.