Michael J. Fox's middle name is Andrew. He needed to use a middle initial, because an actor named Michael Fox already had a Screen Actors Guild card. But he was afraid, as a Canadian, Michael A. Fox would be mocked (Michael "Eh?" Fox).
Ulysses S. Grant was born Hyram Ulysses Grant, but the Congressman who'd nominated him for admission to West Point mistakenly used the name Ulysses S. Grant, which stuck.
Here are the full names of other initial-using people.
"¢ John Ronald Reuel Tolkien
"¢ Clive Staples Lewis
"¢ William Frank Buckley, Jr.
"¢ Hunter Stockton Thompson
"¢ George Gordon Battle Liddy
"¢ Presidents include James Knox Polk, Rutherford Birchard Hayes, Chester Alan Arthur, Warren Gamaliel Harding and Richard Milhous Nixon
"¢ George Campbell Scott
"¢ Elwyn Brooks White
Eedward Eestlin Ccummings
"¢ Philip Kindred Dick
"¢ Homer Jay Simpson
"¢ Booker Taliaferro Washington
"¢ Alan Whitney Brown (A. Whitney Brown joked that, one day, he hoped to be THE Whitney Brown)
"¢ Howard Kevin Stern (not the Sirius radio host, Anna Nicole's lawyer)
"¢ Patrick Jake O'Rourke
"¢ Mary Jane Blige
"¢ Joanne Kathleen Rowling (or maybe not)
Now you know. And if you know of others, fill up the comments.