It may not come as a huge surprise that communist and anti-capitalist philosopher Karl Marx died a poor man.

But why did the German, who had seven children by his wife and died in north London, leave his meagre £250 (£23,000 today) to his youngest daughter Eleanor?

New online records are offering tantalising insights into the financial affairs of famous figures from the 19th and 20th Centuries.

Official summaries, or indexes, of more than six million wills from 1861 to 1941 have been put online for the first time.

They took about a year-and-a-half to digitise, and reveal a fortune of more than £20bn.

Once-rich polar explorer Sir Ernest Shackleton left even less than Marx, the records show.

By the time he died in 1922, he was down to £556 (£20,000 today), having lost his fortune in a series of failed business schemes.

Naturalist Charles Darwin, by contrast, left the Victorian equivalent of about £13m today, and Charles Dickens £7m.

Image caption Portsmouth-born novelist Charles Dickens died a rich man on 9 June 1870

The probate calendar books for England and Wales present easily accessible records for historians and academics who have had to rely on paper searches until now.

But they also allow people to research their own family trees and tales of lost fortunes and wealthy ancestors.

Historic feuds and branching family trees mean many mysteries of missing millions will never be solved.

Sir Ernest Shackleton (1874 - 1922) The Anglo-Irish explorer left £556 (£20,000 today) - having lost his fortune in failed business schemes. Best known for the 1914-16 Endurance expedition to the Antarctic, he sought to cash in on his celebrity. But tobacco, mining, and postage stamp ventures all failed and his main source of income was lectures.

But the new online archive claims to bring amateur historians one step closer to discovering the truth.

Searches allow you to find the value of an estate, and learn more about someone's social standing and worldly possessions.

The documents give names, dates and places of death, executors, and in some cases who inherited the estate.

The documents, which originally came from the Probate Office, have been put online by family history website Ancestry, a US company which charges subscribers for accessing the information.

The National Archives, a government agency, has in the past struck up similar licensing partnerships with Ancestry and other private firms to put its public records online.

Audrey Collins, the Archives' family history specialist, said: "Wills are a wonderful resource for family history because they are full of names.

"Better yet, individuals and family relationships were often described in detail, because it was important that the right person got the money - or didn't, as the case may be.

Common name

"Some of the best wills were left by people who named lots of relatives, even if the value of their estate was not very great.

Historic rich list: Some famous names Chocolate producer John Cadbury left £43,773 (£4.2m today) in 1889

Cricketer W G Grace left £7,278 (£620,000 today) in 1915

Scientist Michael Faraday left £6,000 (£500,000 today) in 1867

Author Lewis Carroll left £4,145 (£450,000 today) in 1898

Sherlock Holmes creator Arthur Conan Doyle left £63,491 (£3m today) in 1931

"Spinsters and childless widows often left wills naming all their nieces and nephews, so you should never neglect the females in the family."

She added: "Even indexes on their own are useful, as they usually contain more details than death index entries, so they can help identify the right entry if the person has a common name."

Details of one million wills from 1384 to 1858 - including Shakespeare's - were put online by the National Archives in 2004.

The latest documents date from the period after that, when the administration of wills was transferred from the Church to the state.

Ms Collins added: "There is no single 'one-stop shop' for wills in England and Wales, so the family historian may have to look in a number of different places.

"As more indexes are made accessible, it becomes easier for researchers to find the records that they need, wherever they are kept."

Thomas Holloway (1800 - 1883) The patent medicine seller left one of the largest estates in the index - £600,000 (£55m today). He made his fortune selling pills and ointments, and spent large amounts of money advertising them. Scientific tests after his death showed few of his products contained any ingredients considered of significant medicinal value.

Research by Ancestry suggests more than two million people in Britain - or 6% of the population - claim to know of a wealthy ancestor.

Ancestry director Dan Jones said: "Anyone able to find an ancestor in the probate calendar books will be able to find out a great deal about how their ancestor lived, what they bequeathed and to whom."

The continual digitising of public records shows no sign of slowing down, and in recent years has included documents on crime, immigration, war, education, taxation and religion.

The National Archives says that has been made possible through licensing partnerships with commercial companies as it does not have the funding itself.

It says the funds it receives from the partnership scheme allow it to reinvest in its services.

This latest archive will no doubt throw up some fascinating stories, but will any match the unusual will of Canadian lawyer and financier Charles Vance Millar, a noted practical joker?

He offered the bulk of his estate to the Toronto woman who had the greatest number of children in the 10 years after his death, in 1926.

Attempts were made by his would-be heirs to invalidate it, but the will stood and his fortune eventually went to four women.