A really good book that targets your exact question is Michael Elliott's Custerology: The Enduring Legacy of the Indian Wars and George Armstrong Custer. As Elliott argues and explains, Custer and the Seventh Cavalry's defeat has been interpreted so many times in so many different ways that the memory of the man himself can't help but be affected.

Richard Slotkin's 1985 book The Fatal Environment argues that Custer's Last Stand became iconic because it was a singular moment that defined a global conflict between the forces of "civilization" and "savagery," to use the white Western point of view. The Seventh Cavalry's defeat was a public moment right from the instant it happened. It was covered in all the major newspapers and illustrated journals.

With a presidential election in November of 1876, Custer's defeat became a political issue. Democrats opposing the party of incumbent president Ulysses Grant damned the Republican Party for putting Custer's men in harm's way. Republican newspapers and campaigners retorted that Custer was the one responsible for the defeat through incompetence. As the Chicago Tribune wrote on July 7, 1876, Custer was defeated because he "preferred to make a reckless dash and take the consequences in the hope of making a personal victory and adding to the glory of another charge rather than wait for a sufficiently powerful force to make the fight successful and share the glory with others."

Grant, no small general of his own, said he regarded the battle "as a sacrifice of troopers, brought on by Custer himself, that was wholly unnecessary ─ wholly unnecessary." Official War Department reports, coming from a Republican administration, echoed this account.

But there was an element of martyrdom, as Slotkin argues. In December 1876, a hack writer named Frederick Whittaker championed the idea of martyrdom. In A Complete Life of Gen. George A. Custer, he was first on the scene with a book that compared Custer favorably to Napoleon and called him "one of the few really great men that America has produced."

It helped that Custer's wife spent her remaining years attempting to vindicate Custer, and that Buffalo Bill used Custer's notoriety and fame to his own benefit. Dime novels promoted a link with no truth, and Buffalo Bill's shows used a recreation of the last stand as his show's climax, the better to demonstrate the attractive violence of the West.

In the early years of film, Custer movies were big: They came out in 1909, 1912, 1913, 1921, 1921 and three in 1926.

The biggest Custer memory of all, however, is owed to Anheuser-Busch Brewing. In 1890, the brewery acquired the rights to Cassily Adams' painting Custer's Last Fight, then used it in a marketing campaign that sent more than 150,000 copies to saloons and drinking establishments across the country. No American painting, with the exception of Gilbert Stuart's Washington (used for the $1 bill and distributed to most classrooms in America as part of an early 20th century campaign) has been reproduced more.

But starting about the time of the 50th anniversary of the battle, the historiography started to change. With the skepticism of a post-WWI America, historians concentrated on Custer's problems ─ his vanity, his insubordination, his glory-seeking. Frederic Van De Water's Glory Hunter is perhaps the perfect example of this. It was followed by fiction like Harry Sinclair Drago's Montana Road, which showed a glory-seeking Custer provoking war and foiling the attempts of peacemakers.

The pro-Custer movement waned from the 1920s to the 1940s, and by the end of the 1940s, anti-Custer sentiment had passed it. John Ford's Fort Apache (1948) was the first big anti-Custer film. Through the 1950s and 1960s, the anti-Custer sentiment accelerated.

By the 1960s, Custer's career was synonymous with oppression and racism. During the Vietnam War, comparisons between that conflict and the Indian Wars became commonplace. By the 1970s, there was a huge surge of interest in the American Indian perspective and point of view, and this did nothing to change the prevailing sentiment that Custer was a fool who got what he deserved, especially as historians examined his military record during the Indian Wars and started taking an appropriate harsh line on the U.S. Army's massacres in the West.

In recent years, the historiography has started to turn again. Newer works recognize Custer's flaws, but they also examine his success during his American Civil War career. More than a few have speculated that Custer's escalating recklessness after the war was linked to his frustrated ambition to become an American hero. With the end of the American Civil War, outlets for that ambition were limited, and Custer's drive forced him into positions and actions that other men shied away from.

Those actions ultimately led to his doom, but they ensured him a place in the history books ─ even if it wasn't the one he wanted.