Complex sentence: He has accrued his wealth from mining, lumber, and investment, and is the majority shareholder of Metalloinvest, a Russian industrial conglomerate, which he founded to manage Gazprom's metals interests.
Split into simpler sentences: He has accrued his wealth from mining, lumber, and investment. He is the majority shareholder of Metalloinvest, a Russian industrial conglomerate, which he founded to manage Gazprom's metals interests.