Samantha (played by Abbey & Kona, two three year old German Shepherds / Alsatians) is a loyal German Shepherd (Alsatian) that beloings to the 'Neville' family.
She plays two very different parts from the Novel and the movie.
Samantha was bought by the 'Neville' family at a very young age (puppy).
She then lived with the family peacefully until 2009, when the outbreak of the 'Dark Seekers happened.
Sam helped Robert try to find the cure to the disease as best as she could, and even at the moment of death, stood loyal towards her owner.
Her death was very tragic, as she got into a fight with some infected dogs, resulting in herself becoming inected, in order to save her owner from getting eaten alive. Robert saved her by shooting the last infected dog, but she was already bitten by the Darkseeker dog and lived for a short time.
Robert rushed back home to his labratory and gave Sam an injection hoping that it wasn't too late, and sat with her.
Sam quickly converted into a Dark Seeker and bit at Robert. This forced Robert to strangle her to death, looking away and feeling highly uncomfortable while doing it.
She was buried in the town as respect from being such a good dog and also so the monsters couldn't get to her body.
Sam doesn't come into the novel until half way through, when she is foud wandering around outside of Robert Neville's house
Soon, she ends up dying from a Dark Seeker.