Enormous losses at Archegos Capital Management have cast a rare spotlight on the growing influence of below-the-radar institutions around the globe called family offices.

These firms, which manage huge piles of wealth for individuals or families, are proving to be increasingly important to the financial system. Just 121 of the largest single-family offices represent an estimated net worth of $142.4bn, according to a report last year by UBS Securities. Sixty-nine percent of these offices were established since 2000, the report found.