Best friends can share anything with each other, even their biggest secrets. These seven pairings played it close to the vest for each other to win wars, rescue royalty, and revolutionize literature.

1. Mark Twain and Helen Keller

You may not have known they were best friends, but despite their 45-year age difference, the pair boasted a friendship Twain described as so special that “I suppose there is nothing like it in heaven; and not likely to be, until we get there and show off.”

In the same letter that he extols their bond, Twain expresses outrage at having learned through Keller’s autobiography that she was accused of plagiarism as a child for a story she wrote. In her defense, Twain claims that it is his belief everything ever said or written is somehow plagiarized. To make his pal feel better, Twain shared a secret of his own: The dedication of his book Innocents Abroad was directly plagiarized from a Dr. Holmes.

2. Meriwether Lewis and Thomas Jefferson

The Lewis of Lewis and Clark expedition fame was given a secret key-word cipher for encrypting messages to send back to the White House during the transcontinental expedition. It’s a complicated algorithm to explain, but their keyword was “artichoke.”

3. Mary Todd Lincoln and Elizabeth Keckley

Keckley was a former slave who bought her own freedom and established a successful dressmaking business in Washington, DC. She eventually became the personal seamstress and confidant to Mary Todd Lincoln during and after her time as First Lady.

The notoriously difficult Lincoln cut Keckley in on the White House gossip, who was said to be “the only person in Washington who could get along with Mrs. Lincoln.” The close relationship was severed when Keckley spilled many of those secrets in an autobiography detailing her experience with the First Family, Behind the Scenes.

4. Nathaniel Hawthorne and Herman Melville

Melville’s big secret: Moby Dick was very nearly a rotten book! Melville practically worshipped Hawthorne, who was fourteen years older, and their friendship eventually saved him from wasting his masterpiece. At the time, the book that would become Moby Dick was a light-hearted tale of maritime adventures. But at Hawthorne’s suggestion, Melville scrapped that draft and crafted his philosophical tome, to be dedicated to Hawthorne.

5. Winston Churchill and Franklin D. Roosevelt

The contents of The Atlantic Charter that defined the Allied goals for World War II are hardly secret any more, but when the two heads of state were first discussing the policy, everything about their August 1941 meetings aboard the USS Augusta had to be surreptitious. Roosevelt announced he was going on a fishing expedition and Churchill snuck away on a battleship to their clandestine meeting off of Newfoundland.

6. Emily Dickinson and Thomas Wentworth Higginson

During the pair’s twenty-four year correspondence (they only met in person twice), most of what the reclusive poet shared with the radical essayist was a secret — including many poems that went unpublished until after her death.

7. Joe Louis and Max Schmeling

In the boxing ring, these two were bitter foes. German-born Schmeling was celebrated after his 1936 victory over the undefeated Louis, one of the first African American sports stars. Two years later, Louis knocked out Schmeling in a rematch fraught with racial implications. But despite the heavily hyped in-ring rivalry, the two went on to be close friends later in life and when Louis’ finances floundered due to tax trouble and unchecked generosity towards family members, Schmeling quietly came to his aid and kept Louis’s financial difficulties to himself.