Complex sentence: Barclay's descendants include David Barclay of Youngsbury (1729--1809), an English Quaker merchant and banker, also known as a philanthropist and abolitionist.
Split into simpler sentences: Barclay's descendants include David Barclay of Youngsbury (1729--1809) was an English Quaker merchant and banker. He is also known as a philanthropist and abolitionist.