Complex sentence: Theisen in 1983 constructed a mansion, at the time the largest mansion in Omaha; he sold the mansion in 1995 to Terry Watanabe, former owner of Oriental Trading Company.
Split into simpler sentences: Theisen in 1983 constructed a mansion, at the time the largest mansion in Omaha. He sold the mansion in 1995 to Terry Watanabe, former owner of Oriental Trading Company.