Complex sentence: Thea Christiansen Foss (8 June 1857--7 June 1927) was the founder of Foss Maritime, the largest tugboat company in the western United States, and the real-life person on which the "Tugboat Annie" series was based.
Split into simpler sentences: Thea Christiansen Foss (8 June 1857--7 June 1927) was the founder of Foss Maritime, the largest tugboat company in the western United States. She was the real-life person on which the "Tugboat Annie" series was based.