I am watching old episodes of Mad Men. I didn't know that Don had told anyone about his past. In this episode when the feds ask Betty soalan in a background check, it appears that he told Pete! When did he tell Pete?? Thank anda for your help!

A package from Adam Whitman (Don Draper's younger brother) arrives at Don's office in Season 1's "Indian Summer", after Pete Campbell had sneaked inside. The package contained imej from Don's past and his real name. Pete got a friend in Federal services to investigate both Don Draper and Dick Whitman and realized that Don was using someone else's identity. He first tried to blackmail Don into giving him a promotion in "Nixon vs. Kennedy". When that didn't work, he told Bert Cooper, who dismissed the matter, because Don was a valuable asset to the firm.

In Season 3's "The Color Blue", Betty was doing the laundry, when she came across a set of keys from one of Don's clothing items. She used one of the keys to open Don's private meja and found the same package that Pete had come across, two years earlier. Betty confronted Don about the items in the box in the following episode, "The Gypsy and the Hobo". He eventually confessed the truth about himself. However, Don pretended that the Army erroneously thought he was the real Don Draper, instead of confessing that he had switched Army I.D. Tag with the real Draper. At first, Betty was willing to go along with his false identity, hoping that this confession would finally help their marriage. But during the Kennedy assassination crisis in "The Grown Ups", she realized that he would never change and decided to divorce him.

Don told Megan the truth about himself between Seasons 4 and 5 - before their wedding. Unfortunately, this has not helped their marriage.

Right now, only four people living know that Don Draper is really Dick Whitman - Betty Draper Francis, Megan Draper, Pete Campbell and Bert Cooper.