Samantha (also known as Sam) is a dog and Robert Neville's only living companion. She is played by two German Shepherd Dogs named Abbey & Kona.
On the night that Robert Neville attempts to evacuate his wife and daughter from the city, his daughter hands him Samantha - then still a puppy - and tells Samantha to look after her dad.
Following the mass evacuation of the city, its isolation - by the destruction of bridges - and the ultimate death and/or infection of every other human in the city, Samantha becomes Robert's sole companion. Throughout the movie it is seen that Robert's bond with Sam is almost human, as he talks to her like a human friend and even feeds her food off of a plate and later berates her - in a loving way - for not eating her vegetables.
Sam accompanies Robert where ever he goes, including on hunting trips. In one tense moment Sam follows a deer into a dark building while hunting and has to be rescued by Robert from a "hive" of Darkseekers.
Heroic fight, Infection and deathEdit
Robert, even though he has Sam for company, clearly shows signs of isolation and the need for human contact as he talks to mannequins and even implies attraction to a female mannequin in a video store. He apologises to Sam for not chatting to the female mannequin, but promises to build-up the courage to do so. While out driving Robert comes across "Frank". He exits his vehicle and becomes angry with "Frank" because "Frank" has moved by himself. He proceeds to shoot the mannequin. He is immediately overcome with grief by his actions and walks over to "Frank". It is then that we realise that "Frank" was placed there as a decoy by Robert as when getting near "Frank", Robert triggers a similiar snare to the one he set to catch the female Darkseeker he is using for anti-virus tests. Robert is knocked unconscious after hitting his head when the snare lifts him off the ground.
Robert is later woken by his watch beeping - warning him that the sun will set soon - and Sam crying and licking his face. Robert manages to cut himself loose but injures his leg when falling. While crawling away, three infected dogs emerge from the building. Sam shows she is ready to fight but Robert manages to keep her relatively calm, knowing the dangers of a bite. As the sun sets, the last sliver of sunlight keeping the infected dogs at bay disappears and they charge after Robert, who has just reached his car. Sam attacks the first dog that arrives while Robert has to deal with the second one. Robert, while fighting with second dog, is clearly concerned by Sam's fight, fearing for her safety. The infected dog viciously bites Sam Robert manages to kill both dogs but is too late to save Sam from serious injury.
Robert takes Sam home and attempts to use his as yet unsuccessful anti-virus on her. After injecting her he sits with her on his lap, pets her and sings to her in a soft voice. At this point he sees that her hair is starting to fall out and notices that her heart rate and breathing has also increased. He checks her pupils - which do not react to light exposure, much like Darkseekers - as well as her gums, which are discoloured. Sam then begins to start growling and attempts to bite Robert, forcing him to strangle her to death, much to his disappointment.
Sam's death has a profound effect on Robert. Not only was she his only form of companionship, but as she was Robert's daughter's puppy, this also implies even further sentimental attachment. Sam's death can be seen as the final loss of any connection Robert has to his daughter and family. Robert later approaches the female mannequin at the video store, telling "her" that he "promised a friend" he'd build-up the courage to talk to her. Distraught that the mannequin cannot respond and that he is finally truly alone, Robert goes on a suicidal rampage against the Darkseekers. When he is resuced by Anna, the effects of Sam's death are still present as Robert loses all hope, telling Anna everyone he loved is dead.
Robert only recovers his hope in the final moments of the film, as he realizes that his anti-virus will work. It's very likely that he sacrificed his life for his family which definately includes Sam.