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I Am Legend Ending Explained

Approximately eighty seconds is all it takes for I Am Legend to jolt from hope to despair. It's all that separates the opening scene showing a doctor announcing one of the biggest medical breakthroughs in history from the zombie apocalypse, which occurs due to a disastrous mutation of that very same breakthrough.

Lieutenant Colonel Robert Neville (Will Smith) attempts to find an antidote to the world-shattering mutation. Through his perspective, I Am Legend is a story of hope wrapped in a layer of post-apocalyptic turmoil with religious overtones. With that in mind, what some feel is a confusing ending becomes far more clear when you understand Neville's personal journey. Warning: Spoilers from here on out—as if you didn't know.

A cure for cancer turned deadly

Created by genetically altering measles, the Krippin Virus had promised to be a "miracle cure." As Dr. Alice Krippin (Emma Thompson) explained in a television interview, if the body were a highway, the virus was reprogrammed from a "very fast car, driven by a very bad man" to one driven by a police officer—one who cured all cancer-ridden patients during clinical trials.

Sadly for the human race, that police officer turned on its citizens. After its initial promise, the reprogrammed virus mutated with catastrophic results. It killed 5.4 billion people, with 5% transformed into zombie- or vampire-like "Darkseekers." One percent of the population remains immune but not exactly lucky—their lives have turned into a constant fight for survival. That 1% includes Neville, a virologist for the U.S. Army. 

Neville remains in New York City after it is placed in military quarantine, due to a strain of Krippin's Virus (KV) turning airborne. The responsibility of saving the human race rests on his shoulders, thanks to his scientific knowledge and high-ranking role in the military.

Isolated in New York

I Am Legend depicts the fallout of the KV virus—a total lack of human survivors. However, in the early moments of the film, Neville personifies the phrase "alone, not lonely." In the three years since the virus spread, he has constructed a world that could almost be mistaken for normality. His daily cooked breakfast precedes his ongoing experimentation, which takes place in a laboratory in the basement of his heavily barricaded home. He has jovial interplay with a set of mannequins, dressed and deliberately placed in his local video store. It's his way of coping, along with the help of his dog companion, Sam.

Though Neville's world-saving quest to find an antidote gives him long-term purpose, his nurturing and caring for Sam gives him a reason to continue day in, day out. Sam provides immediate meaning. This is crucial for Neville's sanity as he embarks on his improbable task. Caring for Sam helps balance his distant hope of salvation with a reason to keep moving forward, despite the grim nature of his situation. Neville's mental resilience and determination motivate him to not drown in the palpable isolation.

The flashbacks

A series of flashbacks slowly reveal events before the quarantine, contextualizing Neville's mindset. These flashbacks depict the critical moment Neville evacuates his wife Zoe (Salli Richardson) and daughter Marley (Willow Smith) with but five minutes to spare. Then tragedy strikes. 

The military air force bomb the Brooklyn Bridge, cutting off the main exit route as part of the quarantine. Amid the chaos, another helicopter collides with Zoe and Marley's helicopter, killing them.

Shortly before her death, Neville had told Marley: "Daddy's gonna make the monsters go away baby, okay?" It becomes clear from that point that present-day Neville is seeking personal salvation in finding the cure; not only for the future of humanity, but so his family's death won't be in vain. This failed escape is the Ground Zero of Neville's motivation, giving him the purpose to survive for these three years spent alone.

The death of Zoe and Marley also explains Sam's value. Shortly before the helicopter takes off, Marley hands off Sam, still a pup, to her father, saying, "Sam can protect Daddy." From that moment on, Sam becomes a living remnant of Neville's old life, the only family member he can love and care for.

"Every little thing is gonna be alright"

Bob Marley's "Three Little Birds" is intertwined with the theme of I Am Legend. A song of hope in itself, "Birds" stands for belief in a brighter future and inspires Neville in times of need. It also facilitates a form of cathartic escapism that guards Neville from insanity. His worries genuinely subside as he sings along to the song while bathing Sam during a heartfelt respite from the danger of the outside world. The singer's positive outlook is the catalyst for Neville's coping mechanism.

His daughter was named after the cultural icon, implying that long before the end-of-world events, the original Marley—who was a devout Rastafari with a deep belief in God—was an inspiration for Neville. 

A conversation at one point with fellow survivor Anna could even suggest Neville chose his career as a virologist thanks to Marley's worldview. He says: "He had this idea—it was kinda a virologist's idea—he believed that you could cure racism and hate, literally cure it, by injecting music and love into people's lives."

He then tells the story of how Marley appeared on stage two days after being shot. When asked why, Neville cites Marley's reasoning: "The people who are trying to make this world worse, are not taking a day off. How can I? Light up the darkness."

Light up the darkness—this becomes Neville's purpose.

The loss of belief

Neville's unflinching resilience enables him to make it this far with his psyche unscathed, despite years of isolation, the death of his family, and the end of civilization. Neville's faith in God's plan is another key ingredient and a link to his family, highlighted when his wife Zoe prays for Neville: "Dear Lord, watch over him." Soon after that comes a turning point. 

In an act of revenge for trapping a Darkseeker for his tests, Neville is ambushed by other Darkseekers, including canines also infected with the virus. After grappling with the infectious ones and escaping to the safety of his home, Neville realizes his dog Sam is infected. Unlike her owner, Sam isn't immune from the KV virus. In a scene that would melt the coldest of hearts, Neville is forced to strangle his best friend and only companion, tragically singing Marley's "Every little thing" whilst doing so.

Sam's death alone doesn't break Neville—it's everything her death represents. She's the tie to his past life, a daily reminder of his motivation to find redemption, and a buffer between being alone and experiencing suffocating loneliness. Neville may even blame himself for not finding a cure in time.

Humanity's late arrival

Rationality is replaced by rage when Neville embarks on a suicidal act of revenge. He sets a trap, waits until nightfall, and when a group of Darkseekers approach, Neville massacres them with his speeding truck. He's outnumbered though and ends up trapped in a wreckage. Just as Neville is about to become an evening snack, a beam of light scares the Darkseekers away.

After three years with no response to his radio broadcast, another face of humanity has finally arrived. But is it too late? Rather than express gratitude for saving him, Neville is dismissive and struggles to communicate.

Above all else, by now his lack of belief is evident. When his savior says she is travelling to a survivor's colony in Vermont, Neville responds in a mixture of anger and hopelessness. "Everybody is dead," he shouts.

When Neville asks how the woman knows of the colony, she replies, "If you listen, you can hear God's plan." Neville's rescuer believes she's following an omen from God, in part because she had turned on the radio in time to hear Neville's broadcast and arrived the day he needed to be rescued. Neville, however, is unconvinced. "There is no God," he tells her.

Finding grace in the butterfly

Previously driven by an unyielding internal faith, it takes a moment of manifested grace to reignite Neville's belief in God's plan. As I Am Legend reaches its climax, the situation becomes desperate when a large group of Darkseekers invade Neville's home. Neville, Anna, and Ethan flee to the basement laboratory for safety. There, in a moment before the chaos continues, they discover that Neville's antidote is finally working.

The Darkseekers make their way to the lab, with one taking lead and smashing himself into a glass partition behind which Neville, Anna, and her son have sought safety. When the leader smashes himself into the glass, the cracks resemble a butterfly, leading to a moment of clarity for Neville. Taking notice of the butterfly tattoo on Anna's neck, he has a realization that this might indeed be divine intervention.

This connects to a gesture from daughter Marley earlier in the film where she says "Look Daddy, a butterfly," forming her hands into a butterfly shape. Neville understands this is no coincidence. He regains his faith in God and His plan.

Self-sacrifice was the only way

After a moment of realization, Neville takes action. He draws blood containing the cure from the Darkseeker test subject and gives it to Anna and her son, telling them to take refuge in a coal chute. Neville doesn't join them.

Achieving validation for the death of his family—in the signs he's seen—Neville is now comfortable paying the ultimate hero's sacrifice to ensure the cure will not be forever lost. He takes a moment to look at a picture of Zoe and Marley—and smiles. Then Neville charges into the onslaught of Darkseekers with a grenade in his hand.

Neville's explosive death fits the religious theme that underpins the film. Choosing to end his life for the greater good echoes passages from the Bible, including John 15:13, which states, "Greater love hath no man than this, that a man lay down his life for his friends." Neville laid down his life not only for Anna and Ethan but for humanity. Additionally, in the Bible, followers of Jesus are asked to sacrifice themselves engulfed in the Holy Spirit, which is represented by fire—much as Neville was engulfed by the explosion, another possible link to the character's Christian faith.

After Neville's selfless final act, Anna and Ethan make it to the colony and hand over the vial containing the cure. Neville is now the titular legend.

The alternate ending

In an alternate ending of I Am Legend, some themes and the story's trajectory are drastically changed. 

Rather than glass cracking in the form of a butterfly, the Darkseeker alpha wipes his own blood onto the glass in the shape of a butterfly. Neville then turns to the Darkseeker test subject on his table, the one he's cured, and notices a butterfly tattoo on her neck. Neville takes a leap of faith and opens the glass partition, risking his life to reunite the Darkseekers. Once Neville's awakened the female, the two Darkseekers embrace in a moment of surprise humanity. 

Smith's character realizes that the mutants, though far from human, are able to express love. From the Darkseekers' perspective, Neville preyed on them, kidnapping and experimenting on their friends, family, and loved ones. He's a legend, but for the wrong reasons—in line with Richard Matheson's book, he is an entity the Darkseekers fear.

Neville doesn't die in this version. Showing remorse for the experiments he has undertaken over the years, Neville, Anna, and Ethan are spared by the Darkseekers. They drive away together, not knowing if a colony exists, but they understand there has been a fundamental shift in humanity. The Darkseekers are now the dominant force.