Martin Gilbert, co-founder and CEO of Aberdeen Asset Management, is a deal junkie. Over the past quarter century, he has built Aberdeen into one of Europe’s leading independent money managers through a series of roughly 40 transactions, ranging in size from the initial tiny £60,000 ($88,000) buyout of an investment trust in Aberdeen, Scotland, that gave the company its name to the £212 million acquisition of Deutsche Bank’s U.K. fund management business four years ago. Gilbert has used the deals to gain heft and expertise while wringing substantial cost efficiencies out of his growing empire. Along the way the CEO has had one big scrape with regulators and some spells of poor performance, but he has never wavered in his quest to build a leading European franchise.

Now, in the midst of the worst market meltdown in decades, the 53-year-old Scot...