You might expect to hear this kind of question in a game of Trivial Pursuit, and if you’re inclined to say “Simpson”, you’re right – sort of.

In truth, Simpson was not part of his name at all and that’s on the authority of the man himself. On June 23, 1864, Grant wrote to Congressman E.B. Washburn with an explanation, politely noting, “In answer to your letter of a few days ago asking what ‘S’ stands for in my name I can only state nothing.” Yes, it’s largely inconsequential minutia, and one wonders why a congressman queried the commander-in-chief of the army over it while civil war ravaged the nation but it’s also a reminder that even the simplest historical questions are often not so simple.

Grant goes on to explain that the misnomer originated from the congressman who assisted his application to West Point. According to Grant, Senator Morris of Ohio had erroneously named him as “Ulysses S. Grant.” Simpson was Grant’s mother’s maiden name and the name of his brother, but had never been in his own. In fact, he was baptized Hiram Ulysses Grant, though known from the very beginning as “Ulysses.”

It seems the last straw was his diploma and commission from the academy, both of which were issued with the erroneous “S.” Apparently, Grant tried to rectify the problem but his efforts to have the S excised from West Point records proved fruitless, so he resigned himself to signing his name that way.

With the benefit of historic hindsight, though, the “S” seems less mistake than prophecy. After Grant’s spectacular victory at the 1862 Battle of Fort Donelson, his initials were said to stand for “Unconditional Surrender,” in honor of his demand for the same from the confederate forces. The nickname stuck, and Grant continued to live up to it, until finally, on April 9th, 1865 — 149 years ago today — Lee surrendered to Grant at Appomattox Courthouse, effectively ending the civil war.