Helena

Helena is one of the true vampires much like Alucard and Incognito. She appears to be a very young girl but in reality she's extremely old. It is a possibility that she is hundreds of years old, represented by the fact that she has a very 15-17th century appearance, and also the fact that her house is lacking anything electronic/modern. She was turned into a vampire when she was about 8 to 10 years old.

Helena lives on a rooftop apartment where she listens to classical music and enjoys reading books. Seras looks up to her and Helena inspires Seras to realize that she is a vampire. Despite this, Helena seems to hate the Hellsing Organization as she claims to have lost many friends to their "butchery" over the years, although, she appears to hold no personal grudge towards Seras.

She seems very caring, and yet very sad. For as long as she has been a vampire she has grown tired of not being able to die. Helena preferes her solitude and keeps to herself in her house, it could be for this reason that Hellsing and the authorities have, for the most part, left her alone as she appears to pose no real threat to the general populace.

When Incognito came to England, he realized that she could be a threat to his plans so he attacked and devoured Helena soon before Seras arrived to visit her. However despite his power, Helena was able to nearly force her way out of his body but he beheaded her. Seras was distraught at not being able to save her but Helena comforted the young Draculina, telling her not to be sad as she was now finally able to die. In her last words she told Seras to be a loyal and worthy companion to her master and to destroy Incognito, warning of his trap.

After Seras left, Helena's remains were destroyed when her home caught fire and burned down. Her final wishes were realized when Seras helped Alucard defeat Incognito and his minions, thus avenging Helena and allowing her to rest in peace.

Trivia
It is interesting to note that Helena has a name similar to that of Helena's Nail a weapon used by Alexander Anderson.