Dr. Thomas Clark Durant, M.D. (February 6, 1820 – October 5, 1885) was an American financier and railroad promoter.
 He was vice-president of the Union Pacific Railroad (UP) in 1869 when it met with the Central Pacific railroad at Promontory Summit in Utah Territory.
 He created the financial structure which led to the Crédit Mobilier scandal.
The Crédit Mobilier scandal of 1867, which came to public attention in 1872, involved the Union Pacific Rail Road and the Crédit Mobilier of America construction company in the building of the eastern portion of the First Transcontinental Railroad.
 The scandal was in two parts.
 The construction company charged the railroad far higher rates than usual, and cash and $9 million in discounted stock were given as bribes to 15 powerful Washington politicians, including the Vice-President, the Secretary of the Treasury, four senators, and the Speaker and other members of the House.
Oliver Ames (February 4, 1831 – October 22, 1895) was an American businessman, financier and politician from Massachusetts.
 He was the son of Oakes Ames (1804–1873), a railroad baron behind the construction of the Union Pacific Railroad (UP) who was notably censured in the Credit Mobilier scandal for actions taken while a United States Congressman.
 Ames was executor of his father's estate, and took over many of his business interests.
 A Republican, he served as the 35th Governor of Massachusetts (1887–1890).
 He was a major philanthropist, especially in his hometown of Easton, which is graced by a number of architecturally significant works by H.H. Richardson as a result of his influence.
Jacques Laffitte (24 October 1767 – 26 May 1844) was a leading French banker, governor of the Bank of France (1814-1820) and liberal member of the Chamber of Deputies during the Bourbon Restoration and July Monarchy.
 He was an important figure in the development of new banking techniques during the early stages of industrialization in France.
 In politics, he played a decisive role during the Revolution of 1830 that brought Louis-Philippe, the duc d'Orléans, to the throne, replacing the unpopular Bourbon king Charles X. Laffitte was named president of the new Citizen King's Council of Ministers and Minister of Finances (2 November 1830 - 13 March 1831).
 After a brief ministry of 131 days, his "Party of Movement" gave way before the "Party of Order" led by the banker Casimir-Pierre Perier.
 Laffitte left office discredited politically and financially ruined.
 He rebounded financially in 1836 with his creation of the "Caisse Générale du Commerce et de l'Industrie", a forerunner of French investment banks of the second half of the 19th century such as the "Crédit Mobilier" (1852).
 The " Caisse Générale" did not survive the financial crisis caused by the Revolution of 1848.
Crédit Mobilier (officially the Société Générale du Crédit Mobilier, or General Society of Home Credit) was a French banking company, and one of the most important financial institutions of the world during the mid-19th century.
 It had a major role in the financing of numerous railroads and other infrastructure projects by mobilizing the savings of middle class French investors as capital for vast lending schemes.
 The Crédit Mobilier investments created vast debts for the countries which accepted these infrastructure loans and was thus indirectly involved in the European occupations of the countries whose governments defaulted on these loans during the worldwide economic depression of the 1870s.
The F. L. Ames Gardener's Cottage is a small residential house in North Easton, Massachusetts.
 This building was designed in 1884 by noted American architect Henry Hobson Richardson and built the following year.
 This building sits on the original Ames estate and was designed soon after the neighboring Ames Gate Lodge (also a Richardson design).
 Frederick Lothrop Ames also commissioned Richardson to build the nearby Old Colony Railroad Station.
 Two other notable buildings in North Easton, the Ames Free Library and Oakes Ames Memorial Hall, were also Richardson designs and commissioned by the Ames family.
William West Durant (1850–1934) was a designer and developer of camps in the Adirondack Great Camp style, including Camp Uncas, Camp Pine Knot and Sagamore Camp which are National Historic Landmarks.
 He was the son of Thomas C. Durant, the financier and railroad promoter who was behind the Crédit Mobilier scandal.
Oakes Ames (January 10, 1804 – May 8, 1873) was an American manufacturer, capitalist, and member of the United States House of Representatives from Massachusetts.
 As a congressman, he is credited by many historians as being the single most important influence in the building of the Union Pacific portion of the transcontinental railroad.
 He is also noted for the subsequent scandal that alleged the improper sale of stock of the railroad's construction company.
The Ames Monument is a large pyramid in Albany County, Wyoming, designed by Henry Hobson Richardson and dedicated to brothers Oakes Ames and Oliver Ames, Jr., Union Pacific Railroad financiers.
 The brothers garnered credit for connecting the nation by rail upon completion of the United States' First Transcontinental Railroad in 1869.
 Oakes, a U.S. representative to the United States Congress from Massachusetts, asserted near total control of its construction, whereas Oliver became president of the Union Pacific Railroad (1866 - 1871).
 In 1873 investigators implicated Oakes in fraud associated with financing of the railroad.
 Congress subsequently censured Oakes, who resigned in 1873.
 He died soon thereafter.
Grantism became a byword for political incompetence, corruption and fraud during the 1870s, while Ulysses S. Grant was President of the United States.
 The 1869–1877 presidency of Ulysses S. Grant was marred by many scandals and fraudulent activities associated with persons within his administration, including his cabinet, that was in continual transition, divided by the forces of political corruption and reform.
 Among them were: Black Friday, corruption in the Department of the Interior, the Sanborn incident, and the Whiskey Ring.
 (The Crédit Mobilier scandal, although exposed during his tenure, is not considered a Grant scandal.)

Question: What railroad for which Oakes Ames is credit as being the single most important influence in building was caught up in the  Crédit Mobilier scandal?
Answer: the Union Pacific Rail Road