In late 1977, Carl de Geer became seriously ill and passed away in the beginning of 1978. Claes Dahlbäck became CEO; Marcus Wallenberg became chairman. Investor moved to Arsenalsgatan 8C on Blasieholmen, our headquarters in Stockholm today.
 
In the beginning of the 1980s, the Wallenberg family and the Wallenberg sphere owned 19 percent of Investor, 19 percent of Providentia and 14 percent of Export-Invest. Investor and Providentia in turn, owned 40 percent and 19 percent respectively, of the Swedish metal manufacturer Garphyttan which was bleeding from a structural crisis. This time Marcus Wallenberg stepped in and started to execute the necessary actions for Garphyttan. A leading Swedish business magazine, Affärsvärlden, wrote about it afterwards: "The fact that Garphyttan survived was solely thanks to the Wallenbergs' ownership philosophy." The patience and the program of cutbacks implemented in 1981 were Garphyttan's rescue.

Peter Wallenberg becomes chairman and more deals
1982 would be the last year of Marcus Wallenberg's 83-year-long life, and one of the things he accomplished that year was the sale of the Diligentia real estate company. A player on the market wanted to sell its stake in SKF, and the buyers were Investor, Providentia and Skånska Cementgjuteriet, but to manage the purchase, Investor was forced to borrow an appreciable amount of money. Since Investor held approximately 13 percent of the voting rights in Diligentia (Providentia owned 16 percent), Marcus started to look for a buyer for Diligentia, which ended up being the Trygg Hansa insurance company. Investor made SEK 90 m. on this deal. When Marcus passed away, Peter Wallenberg succeeded his father as chairman of Investor in 1982 and was immediately involved in several major deals.

In 1984, Investor and Providentia bought back Volvo's shares in Atlas Copco and Stora Kopparberg. The acquisition was made through Patricia, a company formed especially for the buyback. After that and in the next few years, Stora Kopparberg acquired first Billerud and Papyrus and then Swedish Match and Feldmühle. After these acquisitions, Stora Kopparberg, STORA, became the third largest forestry company in the world.

STORA's offer for Swedish Match was at the time the largest cash deal in history of the Stockholm Stock Exchange. STORA's offer for the entire company was approximately SEK 6 billion.