Ill Ratt

Ill Ratt (病気のラット, Byōki Ratto) was a member of the SPK who acted as a spy for Mello.

Plot.
After the founding of the SPK, Ratt walked outside their HQ and asked a citizen to borrow his phone so that he could inform Mello with information on the Death Note that he had found.

Ratt was briefly seen being ordered by Steve Mason to get John McEnroe to pick up Soichiro Yagami and his daughter Sayu, who was kidnapped by Mello and the Mafia as a trade for the Death Note. After Mello obtained the notebook, he used it to kill Ratt, along with half of the other SPK members, by making him commit suicide by shooting himself in the head with a gun.

Conception.
In Death Note: How to Read 13, Takeshi Obata said that while designing the SPK members, he drew Ratt as being "suspicious looking" to further his character as a spy.

Trivia.

 * In Rewrite 2, instead of committing suicide, he is controlled by Mikami to (unsuccessfully) shoot Near before dying himself.
 * In the anime, he is not revealed to be a spy.
 * Ratt's real name was Carl Darlingbin in the Japanese version, and Sean Darnovey in the English version.