Okay kiddo, Feargal O'Rourke is a person. He's a lawyer who works with really big companies to help them with their money and taxes.
Think of it like this: when you get your allowance or birthday money, you might give some of it to your parents to hold onto for safekeeping. Feargal helps big companies do that with their money, but it's way more complicated because the companies have lots and lots of money.
So, Feargal makes sure that these companies follow all the rules about how to use their money and pay their taxes. It's really important because if they don't follow the rules, they might get in trouble with the government.
That's basically what Feargal O'Rourke does - he helps big companies with their money and taxes to make sure they don't get in trouble.