"What's in a name?" asks Juliet in William Shakespeare's famous tragedy.

Hopefully very little for the thousands of Johns, Roberts, Marys and Susans whose numbers are diminishing rapidly, according to data on baby names since the 1900s.

Few names over the past century have scaled the heady heights of John. And few have endured such a fall from grace. The Hebrew name meaning "God is gracious" was the most popular boys' name of the 1940s – an average of 3083 Johns were born each year that decade. But by 2014, this had dropped to only 107.

Robert and Peter have suffered similar fates, plunging from 2300-2500 babies a year in the decades that each held the top rank to fewer than 100 in 2011.

Among the critically endangered girls' names are Margaret, Mary, Susan and Karen.

Margaret, the most popular name of the 1940s, has tumbled from more than 1600 a year at the peak of its popularity to fewer than 20 a year since the turn of the century.

Susan and Karen are even closer to extinction, having toppled from peaks of more than 1100 a year to fewer than 10 in 2011.

Whether Peter, Susan and Karen will go the way of Dorothy, Betty or Ernest remains to be seen. The birth rates of the latter three had dwindled to fewer than five a year by the 1980s, with scant sign of a recovery.

But as history has shown, in the world of names something that appears dead might just be sleeping.

If the Johns and Marys of NSW are hoping for a resurgence, they could do worse than follow in the footsteps of comeback kids Jack, Grace and Ruby. All three were teetering on the brink of extinction mid-last century but have since risen from the ashes.

Fewer than 10 Jacks a year were born in the 1960s and 1970s. However, a meteoric ascent saw him skip from a rank of 61st in 1987 to first in 1997. He wore the crown of most popular boys' name from 2004-2008, and was the third most popular boys' name in 2015.

Ruby has similarly clawed her way back from the edge of extinction, soaring from a rank of 58th in 2000 to first in 2012.

No name is guaranteed to live forever but the heat maps below suggest a handful with little to fear.

They shows the most popular names since 1960, by rank (1 to 100). Names that made the top 100 of that year are marked by a coloured rectangle; the top ranked name is marked in yellow. Names are ordered from most to least popular, measured by total number of babies born between 1960 and 2014.

Just seven names (five boys' and two girls') have made the top 100 every year since 1960. Among the boys are Matthew, Daniel, William, Joseph and George; among the girls: only Elizabeth and Anna.

Girls' names tend to have shorter lifespans than boys' names, as shown by the larger areas of white on the girls' heat map. (A white patch indicates where a name has missed out on a top 100 ranking.)

Twelve girls' names and 10 boys' names have held the top spot over the 55-year period.

Jessica is the undisputed queen, boasting the longest reign of any name. The Hebrew name meaning "rich" was the most popular girls' name for 14 consecutive years, from 1984 to 1997.

Among boys' names, three stand out for their enduring popularity. Joshua has enjoyed the longest reign, spending a total of 11 years in the top spot (1992-1996 and 1998-2003), while both David and Michael held the top spot for nine years.

David boasts the longest unbroken run in first place of any boys' name, from 1962 to 1970, while Michael ranked first every year from 1974 to 1983, except 1982.

Explore the NSW Registry of Births, Deaths and Marriages interactive (desktop users only) by typing a name below: