Both ranked among the 10 most popular U.S. baby names in 1940, finds the study conducted by family history website findmypast.co.uk to mark the release of the 1940 Census records 2nd April. Today they top the endangered list.

Yet, they are also now suddenly again both the names of the moment, since Donald (“Don”) and Betty Draper have just returned to our screens in Mad Men, Series 5, on Tuesday 26th March.

Plus, Donald Sutherland plays the villain in ‘The Hunger Games’, (released on 23rd March), while Betty White has just been named America’s favorite Hollywood star and the latest recruit into the Broadcasting Hall of Fame.

Their namesakes, however, are now dying breeds. Donald was the ninth most popular name for American boys born in 1940 but now ranks just 377th. Betty was the fifth most popular name for American girls born the same year but no longer even makes the top 1,000.

“Baby names are like period pieces”, says Josh Taylor, a leading genealogist and spokesperson for findmypast.co.uk. “Some recall a particular era, which can make them useful clues for researching family history.

“Indeed, you can sometimes guess roughly when someone was born simply by their first name. In such cases, names can be to genealogy what carbon-dating is to archaeology.”

Carol, Shirley and Ronald are other names from the 1940 top ten now on the endangered list.

Findmypast.co.uk researchers trawled the records of the US Social Security Administration, which has recorded baby names, based on Social Security applications for births, since 1879.

At the time of the 1940 Census, Mary and James topped the U.S. rankings for baby names. But Betty and Donald were both close behind, while Donald Duck, Betty Boop and Betty Crocker were all American cultural icons.

In the years since 1940, however, Betty has fallen farther and faster from favor than any other name, male or female. Ranked the fifth most popular girl’s name in 1940, it was the first of the 1940 top 10 to drop entirely from the top 1,000, which it did in 1997. Carol followed in 2007 and Shirley in 2009.

Yet, in the Forties themselves, Betty’s flourished.

Betty White spent the decade working in radio, eventually getting her own show. This was despite the disruption to her career from World War II, when she joined the American Women’s Voluntary Service. Now 90, she is more popular than ever – the last of the red hot Betty’s.

1940 was also the heyday of Betty Grable, who was about to become America’s favourite pin-up girl in World War II, between starring in a string of hit musicals.

Meanwhile, the cartoon character Betty Boop made her debut in 1930, going on to enjoy a glorious decade.

“In 1945”, says Wikipedia, “Fortune magazine named Betty Crocker the second most popular American woman.” Eleanor Roosevelt was first, but then she had the advantage of actually existing, while Betty Crocker was an invented character, whose first name was originally chosen in 1921 because it had seemed to its parent company “a cheery, all-American name” (while Crocker was the surname of one of the firm’s directors).

In fact, Betty was already in decline by 1940. It ranked second only to Mary during the first half of the 1930s, slipping to fourth for most of the late 30s and then fifth in 1940.

Over 23,000 American babies born in 1940 were named Donald. Donald Trump was a forties baby (born 1946), who these days styles himself “The Donald”. Yet, as a boy he would merely have been “a Donald” – one of several in his school, all growing up hooked on the antics of their near contemporary, Donald Duck (born 1934).

These days, on the other hand, a boy named Donald would be an oddity.

The best-known “Donalds’ in American life were born in the decades either side of 1940: Donald Rumsfeld in 1932, Donald Duck in 1934, actor Donald Sutherland in 1935 (albeit in Canada) and Donald Trump in 1946.

Almost the only exception is Donald (“Don”) Draper, fictional hero of Mad Men, who was born in 1926. But then Donald Draper is, of course, only an alias. His given name at birth was ‘Richard’ (as in Richard Whitman), which has also plummeted in popularity. In 1940, it was the fifth most popular name for baby boys. In 2010, it ranked 127.