One of the most important elements of a story besides the setting is the characters. With historical fiction and especially alternate history novels, it can be tempting to include a historical figure in the story, whether as a side note or as a main character. However, the inclusion of historical figures in an alternate history story is a somewhat divisive tactic among readers of the works. If a story is trying to be plausible, then a writer has to watch which characters they include. For instance, in a story where Rome never fell and colonized the New World, having Abraham Lincoln pop up in the story can be jarring to the reader and break their immersion in the setting.
While the above example may be fairly obvious in breaking the suspension of disbelief, in some cases it might not be so clear. Much of this can also lie with the reader’s interpretation of the butterfly effect. Strictly speaking, any historical figure born at least a year after the point of divergence of an alternate history should not exist, or at least not exactly the same as real history. Minor changes in personal routines could cause the date of conception to be different, and chaos theory says that in all likelihood different sequences of DNA will be passed down from the parents, resulting in the person having a different appearance. Additionally, as the timeline begins to diverge further from our history and changes build, the person may have rather different childhood experiences which may lead them to have a completely different personality in adulthood. For instance, Henry Ford’s father William emigrated to the United States in 1846 during the Great Famine. Ford was born almost twenty years later in 1863. If the famine had not happened or occurred in the 1860s instead, Henry Ford would have had a very different life growing up in Ireland or experiencing immigration to the United States firsthand (assuming he is still even born).
However, following the strictest sense of plausibility can interfere with an author’s attempt at an interesting narrative. A complete Axis victory in World War II is certainly not very plausible, but the setting makes for good stories about life under oppressive authoritarian governments in a way that connects with the reader. Similarly, historical figures allow the reader to recognize a character right away and immediately get an idea of their personality and mannerisms. This may seem like a sign that an author is being lazy, but when used in moderation it gives the reader a familiarity with the setting. This is especially useful in short stories. In a short writing space, the backstory of a character may be too long to present in the story, so using a recognizable historical figure imprints the background in the readers mind. Additionally, more obscure historical figures can give a subtle nod to more historically savvy readers. This is often used with people who have changed names or adopted more well known pseudonyms, such as Marion Mitchell Morrison for John Wayne or Lev Bronstein for Leon Trotsky.
So while it may not be plausible, the inclusion of historical characters can be very beneficial to an alternate history story. It gives the alternate history setting a sense of familiarity that cannot be conveyed through other means. When the reader is able to make a connection like this to a character, they will sympathize with the character. The reader may also enjoy the work more as they become more immersed in the story’s surrounding world. However, it is important to not overuse real people. Too many historical figures in a story where it is not likely they should be in the situation can overshadow the original characters of the story, or the buildup of so many real people in the single story can break the reader’s immersion in the world.