When did Dukat become evil?

During "The Maquis, Part 1 & Part 2" he seemed genuinely interested in making the treaty between The Federation and The Cardassians work.

And yet by Series 4, Series 5 he seemed genuinely determined wipe out The Federation, and to reconquer Bajor. And the less said about his time with The Pah-Wraiths the better.

So was he just faking it during "The Maquis"? Or did something cause him to flip a switch (so to speak)?