AFAIK this is his record:
date event venue # car result 1906, Jun 26-27 Grand Prix de l’A.C.F. Le Mans 12C Hotchkiss HH retired 1906, Oct 06 W.K. Vanderbilt Cup Long Island 6 Hotchkiss HH retired 1907, Jul 02 Grand Prix de l’A.C.F. Dieppe BC3 Clément-Bayard 9th 1907, Sep 02 Coppa Velocita di Brescia Brescia 4C Clément-Bayard retired 1908, Sep 06 Coppa Florio Bologna 16 Clément-Bayard retiredI read he was a rich amateur racer with connections to the famous Vanderbilt family.
After some intensive googling I found more than I expected (although I’m still not certain whether he was Elliot or Elliott).
Indeed he was a cousin to William Kissam Vanderbilt II (1878 – 1944) because his mother Margaret Louisa Vanderbilt (1845 – 1924) was a sister to Willie K.’s father (1849 – 1920) [and also to Cornelius Vanderbilt II (1843 – 1899), the father of Alfred Gwynne Vanderbilt (1877 – 1915)]. Margaret was a daughter of William Henry Vanderbilt (1821 – 1885) and a grand daughter of Commodore Cornelius Vanderbilt (1794 – 1877).
You can get an overview about the Vanderbilts here (including a famous portrait painting of Margaret).
In 1868 Margaret Vanderbilt married Elliott Fitch Shepard (1833 – 1893).

Apparently their first daughter, Florence, who was born in 1869 only lived briefly. But they had five more children:
Maria Louise (1870 – 1948), later married to William Jay Schieffelin,
Edith (1872 – 1954), later married to Ernesto Giuseppe Fabbri,
Alice (1874 – 1950), later married to David Hennen Morris (1872 – 1944, founder of the Aero Club of America and of the Automobile Club of America),
Elliott Fitch Shepard, Jr. (1876 – 1927),
& Marguerite (1880 – 1895).
From an „New York Times“ article (1902) we learn something about Elliott Jr.’s youth:
His father, Colonel E.F. Shepard Sr., was known as a lawyer and a newspaper publisher (source).The heir of the Shepards was early inclined to be wild and wayward. While hardly in his teens, stories were told of his escapades. On one occasion, it is said, he disappeared from school and was found in another city, and the tradition is that his father, after giving him a severe lecture, led him to the top story of one of the Vanderbilt houses and administered corporal punishment with a shingle in the good, old-fashioned way. But this story has never been confirmed.
But there's also a different assessment (source).SHEPARD, Elliott Fitch, lawyer, born in Jamestown, Chautauqua County, New York, 25 July, 1833. He was educated at the University of the city of New York, admitted to the bar in 1858, and for many years in practice in New York. In 1861 and 1862 he was aide-de-camp on the staff of Governor Edwin D. Morgan, was in command of the depot of volunteers at Elmira, New York, and aided in organizing, equipping, and forwarding to the field nearly 50,000 troops. He was instrumental in raising the 51st New York regiment, which was named for him the Shepard rifles. He was the founder of the New York State Bar Association in 1876, which has formed the model for the organization of similar associations in other states. In March, 1888, he purchased the New York "Mail and Express."
The following snippets of Elliott Shepard Jr.’s life have been composed from various New York Times articles which can be found on the internet.Elliott Fitch Shepard, whose primary success in life came as a recruiter for the Union Army during the Civil War. Retiring from the military, he failed impressively at both law and banking. He opened a bank at Fifth Avenue and Forty-Second Street which he called "The Bank of Banks." This hubris prompted his father-in-law, William Henry Vanderbilt, to anonymously compose a bit of doggerel for the New York Times referring to Shepard as "The Crank of Cranks."
William Henry Vanderbilt died in 1885, leaving his daughter Maggie $10 million--most of which her husband Elliott managed to run through by the time of his death in various business ventures, including the purchase of New York's Mail and Express newspaper. Another financially expensive undertaking was the purchase of a 600-acre Hudson River estate from Butler Wright. The New York architectural firm of McKim, Mead, and White was hired to design "Woodlea," a new 70,000 sq. ft. manor house that today serves as the Sleepy Hollow clubhouse.
Shepard died in 1893 in a bizarre accident while being examined for kidney disease. Widow Margaret finished the manor house project, hiring the sons of famed landscape architect Frederick Law Olmsted, designer of Central Park to design the grounds.
At the time of his father’s death Elliott Jr. (like three of his four sisters) was a minor. According to his father’s will his mother and his uncle (Augustus D. Shepard) were nominated as his guardians. But at the same time he was, with his mother and his uncle, made trustee of the residuary estate for the benefit of the children and executor of his father’s will although he was not to assume his powers as trustee and executor until he passed his 21st birthday. A peculiar feature in this connection was that while acting as one of the trustees for his sisters he was not to have any control over his own fifth interest.
Elliott Jr. got into a scrape at Yale in 1894, and notwithstanding the influence of the Vanderbilt family, he found it wiser to withdraw from the college and finish his studies under a tutor at Harvard.
He was, however, one of the matrimonial catches of the town. Therefore in April 1897 society was surprised by the announcement of his marriage to a Mrs. Esther Wiggins Potter when he was still only 20 years of age. His wife, the daughter of a storekeeper in Greenport, Long Island, was five years his senior. She had been fifteen or sixteen years old when she married Alfred Potter of Philadelphia. They separated after a year or two, and she went back to her home. When her husband died she came to New York. In the summer or autumn of 1896 she was introduced to Elliott who had just returned from a trip to Europe.
Elliott’s attentions to her had been most marked although unsuspected by his family. After the couple was married by a Justice of the Peace a religious ceremony was performed on April 10th. Mr. and Mrs. Shepard then went to the Plaza Hotel and sailed for Europe on April 15th. The New York Times wrote:
Mr. and Mrs. Shepard never figured in the fashionable world. Until the end of 1901 they were living in London and Paris. Elliott Shepard went into business in Paris, but was not successful. They were not in the least conspicuous in the gay capital. Stories of young Shepard’s financial embarrassment reached New York in 1901, and a sudden trip to Paris by his mother was said to be with the object of helping him.Though Mr. Shepard will have to depend on his mother’s generosity to live in anything approaching affluence, he already has sufficient income under the terms of his father’s will to support him in comfort. […] Heretofore Mrs. Shepard had shown great generosity to her only son, and people in a position to know say that she will continue to do so. When she learned that the young man was irrevocably committed by a civic marriage she insisted upon a religious ceremony, although she was too much prostrated by the news to attend it. The trip to Europe is said to be her suggestion
When Elliott Shepard returned to the USA his wife followed him but visited relatives on Long Island. He was frequently with his mother, and, as his wife had never been received by the family, it was generally stated that a separation had taken place. In August 1902 his wife sued him for absolute divorce. After some time her case was dropped and although there were rumors of a reconciliation they eventually must have separated for good.
As always his mother was most generous to him. He again went to the French capital where he remained most of the time since. He made several business ventures in Paris, all of which resulted disastrously. He tried the liquor business, the banking business, and the manufacture of automobiles, and is said to have lost a fortune in each undertaking. His mother seems to have grown tired of providing capital for him, and at last succeeded in persuading him that he was not fitted for a business career.
On April 27th, 1905, he was driving a 17-hp Hotchkiss along the Avenue Michelet, St. Ouen, and ran over Madeline Marduel, a 12-year-old girl. In October 1905 he was tried in the Correctional Tribunal of the Seine. There was at the time a good deal of agitation against speeding, and Americans in particular were criticised. Maître Poincare, counsel for the prosecution, declared that it was time to stop wealthy Americans from racing about the country and killing peasants. The Judge, in giving sentence on October 26th, echoed the same sentiments and sentenced Shepard to three months' imprisonment, a fine ot $120, and also assessed him in $4,000 damages to the parents of the girl on the ground that the killed girl was a breadwinner.
Shepard appealed the decision. But only in January 1907 the case was settled. After the damages were paid the sentence was reduced to six weeks imprisonment. Shepard spent nine days in the model prison at Fresnes and subsequently the authorities agreed to pardon him on the payment of further $ 2.000.
Meanwhile, after the decision about his appeal had been suspended in March 1906, Elliott Shepard had taken part in no less race than the 1906 French Grand Prix. Maybe he thought if the authorities looked upon him as a racer he would prove it.
To be continued…
Sources: New York Times issues
12 Apr 1893, 13 Apr 1897, 13 Aug 1902, 27 Oct 1905, 13 Mar 1906, 7 Oct 1906, 18 Jan 1907