Shem is a 19-year-old illiterate orphan from Arkansas. He feels a stronger kinship with horses than with people, viewing them as his only true family. He enlists in the Confederate cavalry not for political reasons or to seek military glory, but solely to acquire and care for his own mount. He finds the violent nature of human conflict deeply disturbing, particularly its impact on innocent animals.

Gideon is a literate, free Black man from Cincinnati, Ohio. Frustrated by the Union army's refusal to accept Black soldiers in combat roles, he cuts his hair and uses a large hat to pass as a white man under the alias "Able." He is highly motivated to secure respect for his community and refuses to accept a subordinate labor role, desiring instead to fight on the front lines.

Toby is an eleven-year-old boy from Georgia who lives with his grandfather. Eager to experience battle and secure a glorious reputation, he overcomes his age restriction by volunteering as a military musician, despite not knowing how to play an instrument. He initially views the conflict as a grand adventure and hopes to fight the enemy directly.

Dietrich is a German immigrant from New York fighting for his adopted homeland. Lacking a family of his own, he forms a deep emotional attachment to a photograph of an unknown seamstress who sewed his uniform shirt. He relies on this photograph for mental stability and a sense of purpose during the terror of military marches and battle.

James is a sketch artist working for the New York Illustrated News. His job is to embed with the Union troops and create realistic battlefield drawings for the civilian public. He views the military preparations through a highly romanticized and artistic lens, trusting completely in the Union's superiority and martial virtue.

Colonel Brattle is a Confederate officer and a veteran of the Mexican-American War. Unlike the celebrating civilians around him, he remembers the gruesome reality of combat and feels profound apprehension about the impending conflict. He serves as an advisor to his commanding officers, offering a cautious perspective.

Flora is a grandmother in Virginia who supports the Confederacy from the home front. After sending her sons-in-law off to war, she occupies her time by founding a Soldiers' Friend League to make shirts and bandages. She expects the conflict to be swift and glorious for the South.

Virgil is a young Confederate soldier who deeply resents Northern influence and eagerly anticipates fighting. He travels with his regiment through Virginia, driven by a desire to push back against what he sees as tyranny, though he soon encounters the chaotic and terrifying reality of a large-scale clash.

Dr. Rye is a medical professional attached to the Confederate army. He spends the early days of the war treating soldiers for rampant camp diseases born of filthy conditions. He privately hopes that illness will prevent men from making it to the battlefield, reflecting his deep dread of combat trauma.

Judah is an eighteen-year-old who enlists as a courier in the Confederate army after witnessing a deadly altercation between a hotel owner and a Union colonel. Driven by bitterness over the incident, he serves by delivering urgent messages across the chaotic, artillery-shattered battlefield.

Carlotta is a young enslaved woman forced to cook and do laundry for Confederate soldiers in their military camps. She secretly views the approaching Union army as a potential path to freedom and quietly plans her escape while monitoring the shifting tides of the military conflict around her.

Lily is a young girl living under the rule of her strict, abusive father in Minnesota. She is deeply bonded with her older brother, Patrick. When Patrick runs away to join the Union army, Lily spends her days in the fields, having imaginary conversations with him to cope with her intense loneliness.

Nathaniel is an opportunistic photographer who travels with the army to make a profit. He takes portraits of soldiers wanting to leave a memory behind for their families. He capitalizes on the fear of battle by claiming his camera can capture a departing soul, turning a highly lucrative profit from the anxious troops.

General McDowell is the top commander of the Union forces heading into Virginia. He is acutely aware of his troops' inexperience and lack of preparation. Tasked with invading the South and securing a quick victory, he struggles with the heavy burden of leadership and the logistical nightmares of moving a massive, untrained army.

A. B. is a young Union infantryman from Maine who believes all Southerners are cruel, war-loving villains. He initially treats the march to war like a relaxed holiday, stopping to pick blackberries along the way. His eager and naive perspective shifts dramatically once the confusing and brutal reality of the battlefield sets in.

Edmund is a cab driver hired by rich Northerners who want to watch the battle as a form of weekend entertainment. He drives his passengers, their fine clothes, and their champagne to a hillside overlooking the valley. He observes the sharp contrast between his privileged passengers and the dying soldiers below during the ensuing chaos.

Patrick is Lily's older brother who runs away from his strict, abusive father to join the Union army. He writes to his sister about his poorly made uniform and his regiment's lack of weapons as they near Washington, providing a direct link between the home front and the military reality.

Mr. Bee is a boarding house owner who intensely dislikes President Lincoln and the Union cause. He informs Shem Suggs about the Confederate cavalry recruitment, inadvertently setting Shem on his path to enlistment in the hopes of acquiring a horse.

Greta is a bedraggled but beloved Confederate cavalry horse. She becomes Shem's primary focus and represents his deep bond with animals in the middle of the chaos of the military camp.

Susannah is Flora Wheelworth's eldest daughter. Expecting a swift and easy Confederate victory over the North, she confidently packs clean clothes for her husband to wear during an anticipated victory parade in Washington.

Tuck is Virgil Peavey's best friend and fellow Confederate soldier. The two young men promise to stick together and fight side-by-side as they face the approaching Union army in Virginia.

Grandpap is Toby Boyce's grandfather. He remains behind in Georgia when his ambitious, underaged grandson decides to walk fifteen miles to a recruitment station to join the military band.

The Anonymous Seamstress is a young woman who sewed garments for Union soldiers. She included her photograph and a distressing note mentioning suicidal thoughts in the pocket of a shirt. This unintentionally gives a lonely immigrant soldier a reason to survive, as he links his survival to hers.

General Beauregard is the celebrated Confederate military leader commanding the troops at Bull Run. He is viewed as a gentleman hero by Southern civilians but is considered stubbornly overconfident by some of his own veteran advisors regarding his defensive setups.

Abraham Lincoln is the President of the United States. He directs the Union's military response to the secession and faces intense hatred from Southern sympathizers, as well as impatient complaints from his own citizens following military delays.

General Jackson, nicknamed "Old Lemon-Squeezer" by the troops, is a Confederate general. He draws attention for his rigid, highly disciplined, and strict Christian behavior as he commands troops in the camps prior to battle.

Colonel Ellsworth is a Union commander whose bold action to tear down a Confederate flag leads to a violent confrontation. The event sparks intense outrage and inspires sudden military enlistments on both sides of the conflict.

James Jackson is the owner of the Marshall House Hotel. He violently confronts Colonel Ellsworth for removing a Confederate flag, an action that heavily impacts young onlookers and raises the emotional stakes of the early war.

General Schenck is a Union military officer commanding artillery and infantry forces. He directs the early morning bombardment that officially initiates the active combat phases for his assigned brigade.

Custer is a brave Union soldier who actively assists fleeing civilians. During the frantic retreat from Bull Run, he takes initiative to move overturned wagons out of the road, allowing trapped civilian coaches to escape the active battlefield.

Jeb Stuart is the flamboyantly dressed colonel of the Confederate cavalry. He directs his mounted troops into sudden, aggressive charges against Union infantry during the height of the engagement.

General Smith is a Confederate officer who brings fresh troops to the battlefield by rail. He responds to urgent updates from couriers and rushes his newly arrived men forward to shift the momentum of the ongoing fight.

General Bee is a Confederate officer who attempts to rally his overwhelmed troops. He expresses deep frustration over battlefield miscommunications and perceived lack of support from his fellow generals during heavy fighting.

Jefferson Davis is the President of the Confederacy. He oversees the broad strategic placement of his generals and personally travels by train to observe the shifting tides of the battle.