He has spent around £20,000 and five hours a day for the past 28 years scouring archives, cemetery records and census registers to trace his roots back 1,500 years.
Genealogy is now a hugely popular pursuit, buoyed by the advent of the internet and programmes such as the BBC's Who Do You Think You Are?
During his investigations, Mr Blackmore discovered ancestors including farmers, monks, a Wild West cowboy, Civil War soldiers, a King of France, William the Conqueror and Alfred the Great.
He has now traced and listed 9,390 ancestors and applied to the Guinness Book of Records for the title of the world's largest documented family tree.
Experts say his study is "unique" because most of his research was carried out before the birth of the internet - meaning he had to follow a paper trail.
Mr Blackmore, of Taunton, Somerset, said: "When I started I never planned to go back that far but the more I looked the more interested I became.
"There have been some very frustrating times when I seemingly hit a brick wall. But there is always a way around or over an obstacle and you just have to persevere. "I could go back further into my French descendants but I think I'll leave it as it is."
Grandfather Mr Blackmore, a former perfume company buyer, was placed into foster care along with his six brothers and sisters when their parents Ida and Hubert died three years apart, in 1937 and 1940.
He has now found relatives right back to the Cerdick family in 500 AD and can link himself through 37 generations to William the Conqueror in the 11th Century and 45 generations to Alfred the Great in 880AD.
"The records show that my family were yeoman from around the 10th century when monks first started recording births," he said.
Mr Blackmore's wife Sigrid, 77, has been patient and supportive of his endeavours but he has struggled to enthuse the younger members of his family, he said.
"My grandchildren aren't too interested but I'm sure they will want to know more about their family as they grow older.
"I was never really all that interested in history at school but as you get older you take an interest in where you come from," he said.
Genealogist Nick Barratt, who worked on Who Do You Think You Are?, says Mr Blackmore's family tree could well be a record.
"To research 10,000 family members is a unique and amazing achievement," he said.
"Many claim to have traced their family back to the Domesday Book but have actually used short cuts on the internet.
"To actually follow the paper trail is an incredible feat and I cannot praise it enough."
Mr Blackmore is exhibiting a range of his certificates and wills at Taunton library, Somerset on July 14.
For more information visit www.royblackmore.co.uk
"Worlds Biggest" Guinness World Records