Ryuk is a God of Death (shinigami) who cast his personal Death Note into the human world simply because he was bored.
Despite claiming many times that he is not invested in the events that transpire because of his actions, and is merely a spectator, he regularly takes part in either helping or hindering Light with little to no provocation.
He loves apples.
Powers and Stats
Tier: At least 10-A, Unknown via The Death Note.
Name: Ryuk, Shinigami
Origin: Death Note
Age: Presumably thousands of years old
Classification: Death God
Powers and Abilities: Death Manipulation, Life Manipulation and Absorption via Death Note extending his own lifespan, Immortality (Types 1 and 4), Flight, Invisibility to any that have not touched the Death Note, Dimensional Travel, Invulnerability to some degree, Intangibility to some degree, Fate Manipulation, Probability Manipulation, One Hit Kill, Able to see names of humans above their heads, as well as how much life they have left to live, Resistance to Death Manipulation, Limited Mind Control via Death Note
Attack Potency: At least Athletic Human level (By right of size), Unknown via The Death Note (Death Note instant kills anyone who is not explicitly immortal and impervious to it), Durability Negation with Death Note
Speed: Athletic Human, potentially Superhuman via Flight Speed
lifting Strength: Unknown
Striking Strength: Unknown
Range: Universal (Death Notes are capable of reaping human souls from the Shinigami realm, as seen when Gelus saved Misa)
Standard Equipment: The Death Note
Intelligence: Presumably at least Genius, despite his intelligence only being of above average typically, his life has spanned a very long time, many human lifetimes, and has learned much in that time
Weaknesses: Should he choose to not reap the life of a human before his own alloted time runs out, he will die; note that reaping their life when they should die will grant Ryuk what remains of their life. It is assumed that most shinigami have plenty of time spare, as very few take to reaping. If he can be convinced to kill for someone to save their life when they must die, Ryuk shall die in their place.
Note: Ryuk will not succumb to either notable weakness. Firstly, as stated, Shinigami have many years (an indeterminate amount), an amount that is so high it is considered laughable if a shinigami attempts to gain anymore- just being nervous. Secondly, Ryuk shows little to no care for any human life- not even his ally Light, whose soul he reaped himself.