Complex sentence: In the late 1990s, Larry Elmore approached Weis and Hickman to pitch his fantasy world of Loerem, which they agreed to write about in the "Sovereign Stone" trilogy of books.
Split into simpler sentences: In the late 1990s, Larry Elmore approached Weis and Hickman to pitch his fantasy world of Loerem. They agreed and produced the "Sovereign Stone" trilogy of books.