When Chief Justice John Roberts swore in Joe Biden on Wednesday, for some there was a surprise.
Many did not know that Biden's middle name was Robinette.
The unusual name began trending on Twitter, as social media users asked how he came by the original moniker.
Biden is named after his father, Joseph Robinette Biden Sr, who was in turn named after his mother, Mary Elizabeth Robinette.
Joe Biden was sworn in on Wednesday with his full name - Joseph Robinette Biden Jr
The name Robinette comes from his paternal grandmother: it was Mary Biden's maiden name
It is today a relatively uncommon last name: there are only 10,800 people with the last name Robinette, according to HowManyOfMe.com. Biden is even less common: only around 170 people have that last name.
As a first name, it is even less common - only 1,800 people have the name Robinette.
Mary Elizabeth Robinette was born in 1894 in Maryland.
When Mary married Joseph Harry Biden she took his last name.
Her husband, Joseph, was in the oil business, starting off delivering kerosene and later becoming a salesman at the same company.
Their son, Joseph Robinette Biden, was born in 1915 and went on to marry Catherine Eugenia 'Jean' Finnegan, who was born in 1917 in Scranton, Pennsylvania to Irish immigrant parents.
Joe Biden is pictured with his father Joseph Robinette Biden Sr, who died in 2002 aged 86
Jean was a 'spunky Irish lass with a mind of her own,' according to Joe Biden: A Life of Trial and Redemption by Jules Witcover.
Jean and Joseph were married in 1941.
A year later, on November 20, 1942, the first of their four children was born – Joseph Robinette Biden Jr (who they nicknamed 'Joey').
His paternal grandmother, who provided the unusual middle name for her son and grandson, died aged 48 when the president was only one.
She is buried in Newtonville, Massachusetts.
Joseph Robinette Biden Sr died in 2002 at age 86.
Mary Elizabeth Robinette became Mary Biden, and is buried in Newtonville, Massachusetts
The president's middle name sparked amusement on Twitter.
Kevin Klancy, a radio host and blogger who writes as @KFCBarstool, remarked: 'We elected a dude with the middle name 'Robinette' ???'
Another person tweeted a photo of Barack Obama and Joe Biden running through the White House, with the caption: 'Batman and Robinette'.
'Huge day for Robinette visibility,' tweeted one Twitter user, Ashley Feinberg.
'Shout out to all the Robinettes out there who've been living in the shadows. Your time has come, solidarity with the Robinettes.'
Author Mary Robinette Kowal replied: 'Why thank you!'
Biden is certainly not the first president to have a notable middle name.
Obama's middle name - Hussein - was seized on by his opponents as 'evidence' of what they spun as a dangerously international, anti-American leaning.
President Warren Harding's middle name was Gamaliel.
Harry Truman's middle name was simply the letter S, and Theodore Roosevelt did not have a middle name at all.