The classic American label known for never changing actually changed the face of men's fashion a couple times in the 19th c. with the advent of the seersucker suit in 1830 and the button down shirt (those buttons helped prevent the collar from flipping up into polo players' faces) in 1896. They also dressed many of our commanders-in-chief...occassionally under some absolutely terrible circumstances.
According to the Brooks Brothers site:
At his second inauguration, Abraham Lincoln wore a magnificent coat specially crafted for him by Brooks Brothers. Hand stitched into the coat's lining was an intricate design featuring an eagle and the inscription, "One Country, One Destiny." Sadly, it was also the coat Lincoln was wearing when he was assassinated at Ford's Theater.
Ulysses S. Grant began his association with Brooks Brothers during the Civil War, when he ordered tailored uniforms for the Union officers.
Theodore Roosevelt wore a Brooks Brothers military uniform in his famous march up San Juan Hill.
Herbert Hoover preferred Brooks Brothers henley undershirts.
Franklin D. Roosevelt was frequently seen in a great cape specially made by Brooks Brothers for the U.S. Navy.
John F. Kennedy popularized Brooks Brothers' fashionable two-button suit when he wore it at his inauguration. Two-button Brooks suits were also favored by Gerald Ford and George Bush.
No pun intended, but Richard Nixon was an admirer of the "Brooksgate" clothing collection, a special tailored line designed for the young executive.
Bill Clinton has been seen sporting Brooks Brothers casual wear, including a leather bomber jacket he wore the day following his election as President in 1992.
Personal note: I worked in the Kansas City store during my college summers and bemoaned the terrible women's selections and corporate's (and Corporate America's) growing fascination with casual Friday (ahem, Bill). I spent my days there folding, wishing that someone would come in and help them look more like Ralph Lauren, the very man who created a world based on a word - "Polo" - licensed from, you guessed it, Brooks Brothers.