Aaron Lopez (born Duarte Lopez; 1731 – May 28, 1782) was a Portuguese-born merchant, slave trader, and philanthropist. Born in Lisbon into a converso family, he moved to British America, settling in the colony of Rhode Island and Providence Plantations. Through his varied commercial ventures, Lopez became the wealthiest person in Newport, Rhode Island. In 1761 and 1762, Lopez unsuccessfully sued the colonial government of Rhode Island in an attempt to become a British subject.

Duarte Lopez was born in 1731 in Lisbon, Portugal. He belonged to a family of conversos, Portuguese Jews who had converted to Catholicism, although the family continued to practice Judaism in secret. In 1750 Lopez married a woman named Anna, and within two years she gave birth to a daughter, Catherine. Anna died on May 14, 1762, at age 36. In the summer of 1763, Lopez took Sarah Rivera, the New York born daughter of Jacob Rodriguez Rivera, for a wife. Sarah, 16 years Aaron's junior, would bear him 10 children.

Aaron's older brother José had left Portugal years earlier, began to openly practise Judaism, and changed his given name to Moses. Moses was naturalized in 1740 and granted a license by the General Assembly to make potash in 1753, and he became a successful merchant in Newport. In 1752 Duarte and his family moved to Newport, where they too reclaimed their Jewish identities and became Aaron, Abigail, and Sarah.

Lopez established himself as a shopkeeper in Newport shortly after his arrival. By 1755 he was buying and selling goods throughout Rhode Island and dealing with agents in Boston and New York. One of Lopez's early business interests was the trade in spermaceti, a coveted wax extracted from whale oil used to make elegant candles. Lopez built a candle-making factory in Newport in 1756. By 1760, a dozen competitors had built similar plants in New England. Whalers couldn't supply the factories with enough spermaceti to meet the demand, and the price of whale oil was climbing. In 1761, Lopez joined eight other merchants to form a trust to control the cost and distribution of whale oil.

Lopez expanded his trade beyond the North American coastline and by 1757 had major interests in the West Indian trade. He also sent ships to Europe and the Canary Islands. Between 1761 and 1774, Lopez was involved in the slave trade. Historian Eli Faber determined Lopez underwrote 21 slave ships during a period in which Newport sent a total of 347 slave ships to Africa. By the beginning of the American Revolution, Lopez owned or controlled 30 vessels, engaged in the European and West Indian trade and in whale fisheries.

By the early 1770s, Lopez had become the wealthiest person in Newport; his tax assessment was twice that of any other resident. The reason he was successful was that his business interests were so diverse. He manufactured spermaceti candles, ships, barrels, rum, and chocolate. He had business interests in the production of textiles, clothes, shoes, hats, and bottles. Ezra Stiles, the Congregational minister in Newport and future president of Yale College, described Lopez as "a merchant of the first eminence" and wrote that the "extent of [his] commerce probably [was] surpassed by no merchant in America".

In the mid-1770s, with growing tensions between Britain and its North American colonies, Lopez's fortunes began to decline. The Continental Association enforced a boycott against trade with Britain. In October 1775, a Royal Navy force anchored outside Newport's harbour and the population began to evacuate the city. In early 1776 Lopez relocated to Portsmouth, Rhode Island, then to Providence, Boston, and finally to Leicester, Massachusetts. Historian Marilyn Kaplan describes Lopez's losses during the American Revolution as "monumental."

Lopez supported a number of charitable causes in Newport. He purchased books for the Redwood Library and Athenaeum. He contributed lumber to help build the College in the English Colony of Rhode Island and Providence Plantations (which later relocated to Providence and eventually became Brown University), and he donated land to establish Leicester Academy in Leicester, Massachusetts. It has been said about him that he was 'a man of eminent probity and benevolence whose bounties were widely diffused, not confined to creed or sect.'