Complex sentence: Eventually, the cost of fighting to keep what he believed to be rightfully his, Parker filed for bankruptcy and in 1802, the property was sold to John Mullen, who was interestingly, Parker's millwright.
Split into simpler sentences: Eventually, the cost of fighting to keep what he believed to be rightfully his became too much, and Parker filed for bankruptcy. In 1802, the property was sold to John Mullen, who was, interestingly, Parker's millwright.