When he was young, he wanted to be an engine driver.
He has black hair, and whiskers.
He had a job in the City that kept him busy a lot of the time, financed by his wife's money. He did not share his wife's enthusiasm for socialising, and did his best to avoid her dinner parties and suchlike; she often managed to anticipate his excuses and force him to attend anyway, sometimes by threatening to stop financing his business.
He and his wife did not get on: she objected to his smoking and his uncooperative disinterest in her socialising, he to her socialising, what he considered to be her self-indulgence, and her choice in servants. By the time Christopher was old enough to take notice, they had stopped speaking directly to each other; by the time he was old enough for his first governess, they had stopped speaking at all, and communicated entirely by notes carried between them by servants, even when they were in the same room.
There was a rapid turnover of servants in their house, with no servant lasting more than three months; even the ones he approved of eventually had to get away from the atmosphere, which was all the stronger for Cosimo and Miranda both being powerfully magical (an enchanter and a sorceress, respectively).
He puts a lot of store in horoscopes, which was his downfall: he attempted to use them as a guide to making money on the stock exchange, and lost a great deal instead.
For his eventual fate, see The Lives of Christopher Chant (spoilers).