The Jurassic Park star, 75, spilled the beans in his book Did I Ever Tell You This, sharing that he was actually born Nigel John Dermot Neill.
But it seems he wasn’t all that enamoured with Nigel and when he was 11 he changed his name to Sam.
The star told fans it was the “best decision” he had ever made.
However, Neill certainly isn’t the only celeb to have ditched their birth name, with many taking on monikers they liked better or thought would be better for their careers.
Singer Legend was actually born John Roger Stephens, but when he was younger people started calling him John Legend.
The star said the nickname spread and it got to the point where that was what people knew him as.
“People would introduce me as that,” MTV once quoted him as saying.
“They'd play my records for other people and say, 'Yeah, that's John Legend.' Before I knew it, all these people knew me as John Legend, so I had to kind of decide, 'Am I going to get rid of this name?' Now it's there, and I've got to deal with it.”
Pam & Tommy star James was born Lily Chloe Ninette Thomson.
However, she changed her name after her dad James Thomson died when she was 18, as a way of honouring him.
The actor was a drama student when her musician father passed away in 2008 so decided that she would adopt his first name for her stage name.
Doctor Who star Tennant took inspiration from Pet Shop Boys singer Neil Tennant when it came to picking a new name for himself.
The actor was originally called David John McDonald, but as he was launching his career he discovered there was already a David McDonald in the industry.
Speaking on The Late Late Show with James Corden, he revealed he decided on Tennant after leafing through a music magazine.
"I did my first job at 16 – at 16 years old I didn't know actors, I didn't know how you chose a name,” he said.
Actor, singer and comedian Foxx had a clever reason for picking his moniker.
He was born Eric Marlon Bishop but as he was making his way in the comedy world realised that female comics were often called out to perform first.
With that in mind, he apparently landed on the name Jamie as he thought it sounded as if it could belong to a male or female and would mean he got chosen to perform.
The star picked his surname in honour of comedian Redd Foxx.
The Black Swan star was born in Jerusalem and named Neta-Lee Hershlag.
But as she started to break into acting she changed her name to Natalie Portman.
According to reports, she took her paternal grandmother's maiden name as her stage surname.
Watch: Sam Neill describes Robin Williams as the 'funniest' but 'saddest' person he's ever met