What is a term with a negative connotation that can be used to denote someone who became rich through unscrupulous means?

profiteer

a person who takes advantage of a situation in which other people are suffering to make a profit, often by selling goods that are difficult to get at a high price:

-Cambridge

Profiteers make money "at the expense of the people", "profit from human trafficking ", and often "commit human rights violations".

It is an unfortunate fact that many modern-day familial riches find their origins in profiteering committed by an earlier generation, and with time, well, they somehow become respectable.

Many terms used to describe profiting from "illegal/immoral/unscrupulous" activities tend to be specific to the activity: profiteering, black marketeering, extortion, usury, etc. "Ill-gotten gains" would be a simple way of describing the receipts of those activities, but a word or phrase for the actors that fits all of your examples is slightly more elusive.

However, I would argue that all of your examples could be instances of "racketeering." Although the usual definitions require that the activities are illegal and not just immoral or unscrupulous, that requirement would seem to be met by all of the listed activities, though perhaps to varying degrees: Human trafficking and engaging in the blood diamond trade are certainly illegal activities; circumventing global laws would seem to be necessarily illegal; the exploitation of the people by the Russian oligarchs would be the only example that might straddle the line of illegality, though mostly due to a corrupt government being complicit in their activities. Although Russian oligarchs might avoid legal consequences within Russia through cronyism, bribery, or selective enforcement, they frequently run afoul of international laws by engaging in illegal banking activities, money laundering, fraud, or similar infractions.

In fact, because all of the examples you cited would appear to violate international laws - directly or indirectly - the phrase "international racketeer(s)" might be one possibility for encompassing them. As for the immoral or unscrupulous elements, the notion of a moral or scrupulous racketeer, if not impossible, would be oxymoronic at least.