Werekin, most notably werewolves, are creatures that are not only one species but two at the same time. Some werewolves are either allies with vampires or against them. Another type of Were-Creatures are Werecats. In Hellsing the only two were-creatures are The Captain and Schrodinger from Millennium.
Werewolves
Sometimes also known as Wolfmen, Werewolves are the most well-known of werekin. As their name implies, they have wolf-like traits and are capable of transforming into wolves.
Abilities:
Immortality: The Werewolves are Immortal.
Super Strengh: They possesed Super Strengh.
Weaknesses
Silver: Just like vampires, a werewolf is weak against silver weapons. The most effective method is a silver bullet, but anything silver, including a silver tooth, proves to be potent.
Notable Werewolves
Werecats
Although not as popular as werewolves,werecats said to have many of the same abilities as a werewolf, but with cat-like traits instead of a wolf. In the Hellsing universe, werecats appear as humans with furry cat ears. Warrant Officer Schrodinger, is the only known werecat/catboy in the series.
Abilities:
Omnipresence
Schrodinger is able to exist wherever, however and whenever he chooses. This allows him to bypass all known security systems, travel great distances with a thought, appear in multiple locations at once, and even manifest in Seras Victoria's subconscious mind to speak with Zorin Blitz.
Nigh Invulnerability/Immortality
Schrodinger is able to recover from seemingly any injury, no matter how severe. He had most of his head destroyed at least twice in the series, only to appear perfectly fine in later scenes. Although it is never fully explained in the series, this ability is implied to be an extension of his omnipresence powers; if wounded or killed, Schrodinger simply visualizes himself to be somewhere else, alive and unharmed.
Weaknesses
Perception of Self
According to the Major, Schrodinger's ability to be "everywhere and nowhere" requires him to be able to perceive himself as an individual. If he isn't able to recognize himself, he is "nowhere", and his body fades away completely, becoming "a cluster of imaginary numbers". This weakness becomes the crux of the Major's plan to destroy Alucard; by tricking the vampire into absorbing Schrodinger (and thus gaining his abilities), the Major hoped to erase Alucard from existence by leaving him unable to identify himself among the millions of souls that made up his being.