Complex sentence: Lilly was also known for his philanthropic activities and a founder of the Indianapolis-based Lilly Endowment Inc. along with his sons, Josiah K. Lilly Jr. and Eli Lilly, which has become one of he largest private foundations in the United States.
Split into simpler sentences: Lilly was also known for his philanthropic activities, and founded the Indianapolis-based Lilly Endowment Inc. along with his sons, Josiah K. Lilly Jr. and Eli Lilly. The Lilly Foundation has become one of the largest private foundations in the United States.