Avon, Alastair (whom his friend Hugh sometimes refers to as Justin) is mostly amoral.
He was quite strict in his guardianship of his siblings. But his personal life has been a run of gambling and affairs and duels.
He sort of reforms when he meets Leonie. He is nearing 40 and the reader is given every reason to believe that he has left behind his love 'em and leave 'em days. He initially intends to use Leonie to revenge himself on an enemy. He ends by restoring her position and reputation in society and then marrying her.
Heyer does two things terrifically right: (1) for all his amoral tendencies, Alastair has the class-based conventions of his class/time period. He has a low opinion of peasant-born and base-born individuals, especially those foisted on society. I'm not saying I agree. I'm saying that Heyer captures the cultural mores of a class which will wink its eye at some things but stay absolutely firm on others. It depends on a certain amount of cognitive dissonance but it is very real.
(2) Although Alastair will prove a stern and affectionate husband, he doesn't turn into a sweet, kindly, poetry-spewing dandy. He remains sarcastic and something of a "fixer" through The Devil's Cub, which tackles his son's adventures. His son, a rake, is in fact more morally aware than Alastair. He is a generation younger.
Alastair belongs to the eighteenth-century before the French Revolution. Most of Heyer's romances take place closer in time to Jane Austen's period. But her few earlier romances do a fantastic job capturing the mindset and feel of the time period.
After all, as several characters point out, Alastair and Leonie will do fine together: she's just as indifferent to proper later-Victorian ideals as he is and far more bloodthirsty.
