A number of people learned Don Draper's (Jon Hamm) true identity and real name of Dick Whitman during Mad Men but few knew the secretive ad executive's entire backstory. Don Draper was the handsome and mercurial Creative Director of Sterling Cooper (later Sterling Cooper Draper Pryce and Sterling Cooper & Partners) but despite being twice married, the father of three, and bedding numerous women, Don kept the truth that he was born Dick Whitman a closely guarded secret to preserve the illusion of "Don Draper."
Mad Men doled out Don Draper's origin story to the audience but Don himself remained tight-lipped about who he really was under most circumstances. Richard "Dick" Whitman was the son of a farmer named Archibald Whitman (Joseph Culp) and a prostitute who died during childbirth. After his father died from being kicked in the head by a horse, Dick moved to Pennsylvania with Archibald's wife Abigail (Brynn Horrocks) and a different man, "Uncle Mack." Dick grew up in a brothel before he enlisted in the U.S. Army and was sent to fight in the Korean War. There, Private Whitman met Lieutenant Don Draper (Tony Ruptash), who was killed by a mortar explosion. Lt. Draper's body was burned and unrecognizable. Dick, wanting to leave Korea, switched his dog tags with Draper's and he was then mistaken for the Lieutenant by the Army medics. Dick assumed Don Draper's identity and returned to the United States. He moved to New York to become a used car dealer and a fur salesman who dabbled in advertising. Don met Roger Sterling (John Slattery), who bought a fur coat for his mistress Joan Holloway (Christina Hendricks), and Draper struck up an acquaintance with Roger that got him hired at Sterling Cooper. By 1960, Donald F. Draper was Sterling Cooper's Creative Director, was married to Betty (January Jones), and had two children when Mad Men begins.
Don assiduously guarded the fact that he was really Dick Whitman from everyone, including Betty. Draper did so out of fear that he would be discovered by the U.S. government and imprisoned for desertion, and Don also didn't want to lose the affluent life he built as a powerful Madison Avenue ad executive and all of the perks that came with the job. Still, through his own carelessness and sometimes of his own volition, a number of people did learn that Don Draper was born Dick Whitman throughout Mad Men's seven-season run. However, most people only had fragments of Dick Whitman's history and it's doubtful anyone knows the entire truth that Dick purposely switched identities with Lt. Draper to escape Korea.
Most people who found out the truth about Don learned that his real name was Dick Whitman, but what details they gained about Draper's origins varied. Some, like Don's Mad Men season 1 lover Rachel Menken (Barbara Siff) knew the story that Don grew up in a whorehouse but not Draper's real name. In Mad Men's series finale, Don confessed to Peggy Olsen (Elisabeth Moss) during a phone call that he took another man's name but Peggy didn't learn anything more (though she also had bits of info about Don's past). Ultimately, almost everyone who learned that "Don Draper" was fiction also found out that his real identity was Dick Whitman. Yet despite Don's fears about what would happen if he was found out, everyone who learned the truth ultimately kept Don's secret for him until the end of Mad Men.
Adam Whitman
Adam Whitman (Jay Paulson) was Dick's younger half-brother. Adam and Dick had the same father and the younger sibling idolized Dick, who was a decade older. Dick never returned from Korea and Adam was left wondering whatever happened to him until 1960, when Adam saw Don's photo in the newspaper and recognized "Don Draper" as his big brother. In Mad Men season 1, Adam tracked Don down at Sterling Cooper and he only wanted to be part of Don's life, but Draper couldn't risk Betty or anyone learning the truth. Instead, Don paid Adam $5,000 to go away. Poor Adam was heartbroken and hanged himself. Don didn't learn about Adam's death until later, and Adam sent his big brother a shoebox full of photos and memorabilia of their past that played a critical role in Don's life.
Anna Draper
Anna Draper (Melinda Page Hamilton) was the widow of Lt. Don Draper and the first person to discover that Dick Whitman had assumed her husband's identity. Anna tracked Dick down when he was a used car salesman in the 1950s but they struck up an arrangement that blossomed into a genuine friendship and affection, though never romance. Don bought Anna her house in California and she 'divorced' him so he could marry Betty Hofstadt. In 1964, Don visited Anna and found out she was dying of cancer. Anna died in 1965 and Don mourned her as the only person who ever really knew him. Indeed, Anna apparently knew every detail about Dick Whitman and he kept no secrets from her.
Stephanie And Patty Horton
Patty Horton (Susan Leslie) was Anna Draper's sister and her daughter Stephanie (Caity Lotz) was Anna's niece. Patty already knew about Dick assuming Don's identity in Mad Men season 4 so presumably, Anna let her sister in on the secret and Don had met Patty in the years before Mad Men began. Stephanie also knew Don as Dick when they met in Mad Men season 4 so the Horton family was in on it all along. Stephanie and Don struck up a friendship and she called him for help when she was pregnant in Mad Men season 7. Don and Stephanie also traveled the coastal hippie retreat together in Mad Men's series finale. Don referred to Stephanie as his niece and regarded her as his family, but Stephanie didn't quite see their relationship in the same way.
Pete Campbell
Pete Campbell (Vincent Kartheiser) had a roller-coaster relationship with Don where they were sometimes rivals and sometimes allies. Pete both admired and resented Don but in Mad Men season 1, Campbell was actively trying to ruin Draper's career and ultimately intercepted the shoebox containing Dick Whitman's past that Adam had sent to Don. Naturally, he looked inside it, learning all about Don's past and real identity. Pete tried to blackmail Don with the info but his plan backfired. In Mad Men season 4, Pete opening an account with North American Aviation required Don to receive U.S. government security clearance. Don panicked and had an anxiety attack from the government doing a background check and his own lies on his application form, and he forced Pete to cancel the account to save his secret.
Meanwhile, Pete's wife, Trudy (Alison Brie), also knew about the shoebox, but Mad Men never made clear whether she looked inside it or how much, if anything, she knew about Don's real name and history.
Bert Cooper
Bert Cooper found out that Don Draper wasn't really who he said he was when Pete Campbell tried to blackmail Don and told Cooper that Draper was a deserter who deceived everyone. Cooper shocked both Don and Pete with his response: "Who cares?" Bert noted that there were plenty of successful men with worse histories. However, Cooper did use the fact that he "knows a little something" about Don to his advantage twice, which included forcing the evasive Draper to finally sign a contract with Sterling Cooper. While Bert did know that "Don Draper" was fiction, he didn't actually learn that Don's real name was Dick Whitman - nor did Cooper care to.
Betty Francis
Betty finally discovered the truth about Don in Mad Men season 3 when she broke into the desk in his home office and found the shoebox of memorabilia. Betty, who was already unhappy in her marriage to Don and suspicious of his many affairs, found out that he was really Dick Whitman and she learned that Don was married to Anna Draper when she found the deed to Anna's house. Once he was caught, Don finally came clean to Betty about his past, but Betty never forgave him for his lies and ultimately divorced Don to marry Henry Francis (Christopher Stanley).
Doris
After his divorce from Betty, Don's alcoholism got out of control in Mad Men season 4. During the episode "Waldorf Stories," Don went on a bender after he won a CLIO award. He picked up a woman at a bar and brought her home only to wake up days later in bed with a different woman, Doris (Becky Wahlstrom), a waitress he picked up some point during the weekend. While Don had no recollection of who Doris was, she called him "Dick," so at the very least, he introduced himself by his real name in his stupor. It's unclear if Doris learned anything more about Dick Whitman but he never saw her again regardless.
Faye Miller
Dr. Faye Miller (Cara Buono) was a strategist for a consumer research company that consulted with Mad Men agency Sterling Cooper Draper Pryce in season 4. Faye got romantically involved with Don and he confessed that he was really Dick Whitman during his panic attack about the background check. Faye helpfully urged Don to deal with his secret instead of remaining in hiding, but Don never took her advice. Don eventually broke off their relationship when he proposed to Megan Calvet (Jessica Pare) at the end of Mad Men season 4, but Faye still kept Don's secret for him.
Sally and Bobby Draper
Sally Draper (Kiernan Shipka) idolized her father but as she entered her teenage years she became more and more disappointed in Don. When Don and Megan took the kids to California in Mad Men's season 4 finale, Don brought Sally and Bobby to Anna Draper's home as it was being vacated. When Sally asked who painted "Dick" on the wall, Don admitted that it was his name. Betty told Sally about Anna Draper in Mad Men season 5 and Don occasionally told the kids tidbits about growing up poor on a farm and that his father was a farmer named Archibald. Then, in Mad Men season 6, Don took his kids to see the dilapidated house in Pennsylvania where he grew up. Still, Sally and Bobby only had fragments of info about their dad by the time Mad Men was over.
Megan Calvet-Draper
When Don married Megan, he proved that he learned the crucial lesson not to repeat his mistake with Betty. Don proposed to Megan in Mad Men's season 4 finale, "Tomorrowland," and they were married in the interim before Mad Men's season 5 premiere, "A Little Kiss." During those happy months together, Don apparently told Megan the truth about his past as she casually name-dropped "Dick Whitman," indicating she knew. Whether or not Don told Megan as much about himself as he told Anna isn't clear, but Don's second wife knew more than Betty ever did before she found Adam's shoebox. While Don's marriage to Megan collapsed by Mad Men season 7, it wasn't because Draper kept the fact that he was really Dick Whitman from her.