Werekin

Werekin, most notably Werewolves, are humanoid creatures that can turn into beast-like forms. They are supernatural but not undead, like Vampires or Ghouls.

Werewolves
Also called Wolfmen or Lycans, Werewolves are the most well-known form of werekin.

History
Before the days of Ultimate or even The Dawn, Werewolves were plentiful. In Dawn, when he and a teenage Walter face off against The Captain, Alucard recognizes what he is immediately, indicating he's run into their kind before. Given the Hellsing Organization's mission and purpose, it is possible that they were fully or partially responsible for the near extinction of Werewolf-kind.

Alucard remarks he thought their species had been defeated, implying that The Captain is last of his kind.

Abilities
In general, Werewolves appear to be stronger than Vampires, even the modified vampire Alucard. What they can naturally do and not is unclear, as it is possible the Doktor tampered with Hans' biology, making him modified like Alucard.
 * Superhuman Strength
 * Superhuman Reflexes
 * Thick Skin
 * Wolf Form

Weakness
The only known weakness werewolves have is Silver. Holy water, crosses, and other ceremonial items are completely ineffective against them.

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.

Notable Werecats

 * Schrodinger