In the USA... 2 huge 'private' (unlisted) firms are Cargill & Koch Industries.
Cargill: Cargill and MacMillan families own 85%
Koch Industries: The 2 Koch brothers are worth an estimated $35 billion (2nd only to Warren Buffett & Bill Gates)...
BTW, even Bill Gates has many 'private' investments as does his former partner Steve Allen... Berkshire Hathaway owns many other huge 'private' firms as well...
Greedy when others are fearful. Very fearful when others are greedy - to paraphrase Warren Buffett