Willem Kooyker, a pioneer of investing in commodities, broadened the ownership of his $1.5 billion hedge fund for the first time since it was created almost three decades ago. One of the most powerful and enigmatic traders in the natural resources industry, Kooyker said Thomas Kopczynski, James Wohlmacher, Gus Rossi, and his son Terence Kooyker will join him as owners of Blenheim Capital Management LLC. Blenheim invests in everything from oil to metals and agriculture, and at its height in 2011, was the world’s largest commodities-focused hedge fund. The ownership shakeup is the first since 74-year-old Kooyker, who retains a...