Post a character with a deep and gravelly as well as low-pitched voice

Kunimitsu Tezuka from Prince of Tennishas really deep and mature voice...

First character I thought of was Gaara from Naruto. Voiced 由 Akira Ishida

Song below is of Akira singing.

Akira Ishida also did these voices from 日本动漫 I've watched:
Kent from Amnesia
Satoshi from D.N.Angel
Makoto from Boys Be...
Zeref from Fairy Tail
Katsura from Gintama
Athrun from Gundam SEED
Kei from 果酱 Boy
Natori from Natsume Yuujinchou (<------ LOVE!)
Tsukasa from Shugo Chara!
Hajime from Prince of Tennis

Itachi Uchiha (Naruto Shippuden)

Usami Akihiko (Junjou Romantica)
Sebastian Michaelis (Black Butler)

Erwin from Attack on titan has a mature voice. [the voice actor is the same as Sebastian from Kuroshitsuji]

Pein/Nagato

Zoro from One Piece.

Xanxus from KHR

sven black cat his voice sounds deep

Deep, gravelly and low-pitched:

Takaya Kuroda in any of his roles. If I had to pick one, Hyperion from Saint Seiya Omega comes to mind.

Jouji Nakata as Hody Jones from One Piece and 面包车, 范 Grants from Tales of the Abyss.

Juurouta Kosugi as DarkKnightmon from Digimon Xros Wars.

Hideyuki Tanaka and Yuusaku Yara as Aiolia and Aiolos from Saint Seiya.

Tessho Genda in several roles, including Aldebaran from Saint Seiya and Primus from 变形金刚 Galaxy Force.

Yuuichi Nakamura as Jet from Neo Angelique Abyss.

...Tomokazu Sugita as Taurus Hasgard from Saint Seiya: the 迷失 Canvas. Oh GOD. His "Titan's Nova" killed my brain.

EDIT: Tohru Furusawa as Ingram Prisken from Super Robot Wars OG. He was Nakago in Fushigi Yuugi, too.

Plus then there's always Ikuya Sawaki i.e. Issho/Fujitora from One Piece. ...I think he might actually have the deepest and most gravelly voice out of anyone on my list.

Kuraudo Ooishi from Higurashi no Naku Koro ni's voice fits into that category (plus it makes me think of fried 白饭, 大米 xD)