Continental Army during the Revolutionary War. Hamilton was much impressed with his brother-in-law and described him as "a man of fortune and integrity, of strong mind, very exact, very active, and very much a man of business." At the turn of the 19th century John had also established himself as New York's foremost insurance underwriter. 

John's wealth proved vital to Hamilton and Eliza as he employed Hamilton at various stages and loaned the family significant amounts of money—five thousand pounds at one point—when they fell on hard times. Hamilton relied on his brother-in-law's generosity so much that he once confided to a friend that he was insolvent and resigned to "leave (his) family to the benevolence of others." Noting he trusted especially in the “friendship and generosity” of John Barker Church to take care of his wife and children post-obit. 

After the war John was made the U.S. envoy to France and he and Angelica left the U.S. in 1783 and resided there until 1797. While in France the Churches became friends with the Marquis de Lafayette and Benjamin Franklin—who was then serving as the Ambassador to France—and Thomas Jefferson, who later served as Franklin's replacement. While in Europe John also served as a member of the British Parliament for six years—making him one of only two American Revolutionaries to do so—the other being Henry Cruger.

The Churches returned to America in time for John to have an impact on the fateful duel between Hamilton's oldest son, Phillip, and the lawyer George Eacker in 1801. In "Alexander Hamilton" (the biography Lin-Manuel Miranda based his play on), historian Ron Chernow credits John as "the Schuyler family authority on dueling." John earned a reputation as an experienced marksman and someone who, according to Chernow, "never shrank from a good fight and was not averse to duels." In fact, Alexander Hamilton wasn't even the first member of the Schuyler clan to duel against Aaron Burr. John had already dueled against the future U.S. Vice President to settle a banking dispute in 1799.

And though the musical production of "Hamilton" shows Philip Hamilton seeking the advice of his father concerning the imminent Eacker duel—something he certainly may have done—Chernow notes that Philip actually sought the counsel of his friend, David Jones, and his uncle John in the matter. Chernow writes that "(John) Church advised the young men that Eacker’s insulting behavior demanded a response," but that Philip "should try to resolve his differences amicably with Eacker" before resorting to a duel. Uncle John and David even tried to negotiate a truce with Eacker's second beforehand, but to no avail. Chernow notes that Hamilton "applaud(ed) his brother-in-law’s efforts to stave off bloodshed." After Eacker fatally shot Philip the house he was taken to for treatment belonged to John and Angelica Church. What's more, the pistols used in the Hamilton-Eacker duel were John's own London Wogden pistols—the same pistols used in the Hamilton-Burr duel three years later. 

Before his duel against Aaron Burr, Chernow notes that Hamilton turned to his "trusted, intimate friend" John Barker Church

for help and requested to borrow his brother-in-law's pistols. It's also worth noting that after Hamilton died from the wound inflicted at the hands of Burr by John's own gun, the funeral organizers at Trinity Church erected a stage behind Hamilton's casket and put just two chairs at the center: one for Gouverneur Morris—Hamilton's close friend and a gifted speaker who was delivering the eulogy—and the other for John Barker Church. 

In the decade that followed her husband's death, Hamilton's widow Eliza clung to her sister Angelica and her brother-in-law John for comfort and support—assistance the Churches gave freely. After Angelica died in 1814, John returned to his native land of England and died four years later on April 27, 1818. He is buried at St. James's Church in London.

John Barker Church may never have been a brilliant politician, and, due in part to the many unpaid loans he'd provided others, his estate was only assessed at a modest fifteen-hundred pounds at the time of his death, but by all accounts he was a good friend, a good father, and Angelica's loving husband till the end. 

While only those who knew him can speak to how "fun" he may or may not have been, this much is certain: John Barker Church was anything but boring.