As John Adams told it, the American Revolution didn’t start in Philadelphia, or at Lexington and Concord. Instead, the second president traced the nation’s birth to February 24, 1761, when James Otis, Jr., rose in Boston’s Massachusetts Town House to defend American liberty.

That day, as five red-robed judges—and a rapt, 25-year-old Adams—listened, Otis delivered a five-hour oration against the Writs of Assistance, sweeping warrants that allowed British customs officials to search any place, anytime, for evidence of smuggling.

“It appears to me the worst instrument of arbitrary power,” argued Otis, “the most destructive of English liberty…that was ever found in an English law-book.” Until this case, the 36-year-old lawyer had been Massachusetts’ advocate general. But he resigned rather than defend the writs, then agreed to provide pro bono representation to the merchants fighting against them. Inside the courtroom, Otis denounced the British king, parliament, and nation as oppressors of the American colonies—electrifying spectators.

“Otis was a flame of fire,” Adams recalled years later. “American Independence was then and there born.…Then and there was the first…opposition to the arbitrary claims of Great Britain.”

At the time, Otis was the most brilliant orator in Massachusetts, and one of the most influential protesters against Britain’s colonial laws. But you may never have heard his name. He’s the Founding Father who could’ve been.

Born in 1725 in West Barnstable, Massachusetts, Otis enrolled in Harvard at age 14. He developed a reputation as an eloquent defense lawyer early in his career, successfully defending accused pirates in Halifax, Nova Scotia, and young men in Plymouth accused of rioting on Guy Fawkes’ Day. “He had the orator’s fire and passion,” wrote John Clark Ridpath in his 1898 biography of Otis; “also the orator’s eccentricities—his sudden high flights and transitions, his quick appeals and succession of images.”

In the patriotic version of Otis’ life story, conscience called him to defy British authorities after Massachusetts Governor Francis Bernard used the Writs of Assistance to enforce a long-dormant tax on molasses. But to hear his rivals tell it, a family feud inspired his rebellion. Thomas Hutchinson, the Massachusetts Bay Colony’s lieutenant governor, beat out Otis’ father for the job of chief justice in 1760. The younger Otis went to Hutchinson, “swore revenge,” and vowed to “set the province in flames,” the lieutenant governor claimed in his history of Massachusetts. Ridpath, however, dismissed the story. “The art of political lying was known even among our fathers,” he wrote.

Otis’ arguments at the 1761 trial didn’t win over the court, which upheld the Writs of Assistance. But Bostonians, impressed with his oratory, elected him to the Massachusetts House of Representatives soon after. There, he led patriots’ efforts to challenge a succession of British laws and taxes, gaining more fame with every outspoken defense of the colonists’ freedoms.

He developed a reputation as fiery, brilliant and erratic. Friends called him Furio; his archrival, Hutchinson, dubbed him the Grand Incendiary. “Otis is fiery and feverous,” John Adams wrote in his diary in 1765; “his imagination flames, his passions blaze; he is liable to great inequalities of temper; sometimes in despondency, sometimes in a rage.”

His defiance did more than flame colonists’ passions—it stirred them to actively resist.

He likely didn’t coin the phrase, “Taxation without representation is tyranny,” an overstatement based on John Adams’ paraphrase of his 1661 speech. Nonetheless, Otis deserves credit for advancing the idea behind the phrase, and as time went on his opposition to taxation only increased.

“The very act of taxing, exercised over those who are not represented, appears to me to be depriving them of one of their most essential rights,” Otis wrote in his 1764 pamphlet, “The Rights of the British Colonies Asserted and Proved.” The pamphlet, which argued that Parliament had no authority to tax the colonies unless they were granted seats in it, was debated in Parliament itself. “It is said the man is mad,” declared Lord Mansfield during one debate. “The book is full of wildness.”

In March 1765, Parliament imposed the Stamp Act, a tax on nearly every document printed in the colonies. Otis played a leading role in the Massachusetts legislature’s opposition to the law. And when the Townshend Acts levied new taxes on the colonies and revived the hated Writs of Assistance two years later, Otis and Samuel Adams co-wrote the Massachusetts House’s protest letter, again arguing that Parliament had no right to tax the colonies. An enraged King George III declared the letter seditious and demanded that the House rescind it. “Let Britain rescind her measures, or the colonies are lost forever,” Otis replied. The House rejected the demand, standing by its letter. The governor, furious, dissolved the legislature.

All that defiance damaged Otis’ marriage. Ruth, a loyalist, disagreed with her husband’s politics. “He mentioned his wife – said she was a good wife, too good for him – but she was a Tory,” John Adams wrote in his diary. “She gave him certain lectures.” Meanwhile, as tensions rose in Boston, Otis worried that the colonies would soon reach a boiling point. “The times are dark and trying,” he told legislators in 1769. “We may soon be called on in turn to act or to suffer.”

His words proved all too true. That summer, he learned that the four British customs commissioners in Boston had complained about him in letters to London. Enraged, he accused them of slander in a local newspaper. They were “superlative blockheads,” he wrote, threatening to “break [the] head” of commissioner John Robinson. The next night, Otis found Robinson at the British Coffee House near Boston’s Long Wharf and demanded “a gentleman’s satisfaction.” Robinson grabbed Otis by the nose, and the two men fought with canes and fists. The many loyalists in the coffee house pushed and pulled Otis and shouted for his death. British officers stood by and watched.

Otis was left bleeding. Months later, he still had a deep scar; “You could lay a finger in it,” John Adams recalled. The trauma unhinged his already fragile psyche. He started drinking heavily, expressing regret for opposing the British, and wandering Boston’s streets.

“He rambles,” Adams wrote in his diary in January 1770, “like a ship without a helm….I fear, I tremble, I mourn for the man, and for his country.” By February, Adams wrote, his friend was “raving mad, raving against father, wife, brother, sister, friend.”

Though Otis was re-elected to the House in 1771, he was too mentally troubled to play much of a role. John and Samuel Adams and other friends continued to support and socialize with him, but they weren’t surprised when his mind turned fiery and wild again. That December, his rival Hutchinson wrote, Otis was carried away, bound hand and foot. He spent much of the rest of his life living with various friends in the countryside, alternating between lucid moments and relapses.

The Revolution took a toll on Otis’ divided family. His son, James Otis III, enlisted in the American navy and died in a British prison at age 18. His daughter, Elizabeth, a loyalist, married a British captain and moved to England; Otis disowned her.

Friends and family took up Otis’ banner after he left politics. His peers took on leadership roles in the Revolution that he might have assumed. His sister, Mercy, went from answering his correspondence to organizing political meetings and publishing anti-British political satires—one of the first women in America to write for the public. His younger brother, Samuel Allyne Otis, was the first secretary of the U.S. Senate, serving from 1789 to 1814.

In early 1783, John Hancock, then Massachusetts’ governor, threw a public dinner to mark his friend’s return to Boston. But the speeches and toasts threw off Otis’ mental balance, and his family took him back home to the countryside. There, Otis burned most of his papers. On May 23, 1783, he stepped out of his friend’s house to watch a thunderstorm—and was killed by a lightning bolt.

Otis was “as extraordinary in death as in life,” John Adams wrote upon hearing the news. “He has left a character that will never die while the memory of the American Revolution remains.”