Complex sentence: Posner, who had made a fortune in real estate investments in the 1930s and 1940s acquired a major stake in DWG Corporation in 1966 and having gained control of the company used the company as an investment vehicle that could execute takeovers of other companies.
Split into simpler sentences: Posner, who had made a fortune in real estate investments in the 1930s and 1940s acquired a major stake in DWG Corporation in 1966. Having gained control of the company, he used it as an investment vehicle that could execute takeovers of other companies.