Alastor "Mad Eye" Moody

"CONSTANT VIGILANCE!"
     -- Alastor Moody, quite frequently

Dates: died July 27, 1997 while leading the effort to move Harry before the protection charm on Privet Drive wore off (DH4, 5).
Hair: grizzled dark gray hair.
Eyes: one normal, one magical: vivid blue, moves independently, can see invisible things and through solid objects, including the back of his head.
Voice: growl.
Distinguishing features: missing leg, scarred from many battles with Dark Wizards, magical eye (see above), large chunk missing from his nose from battle with the Death Eater Rosier.
Age: older (perhaps Arthur Weasley's age?).
Field: Auror (retired), Hogwarts Defense Against the Dark Arts teacher 1994-1995.
Devices: magical blue eye, 2 invisibility cloaks (one loaned to Sturgis Podmore and not returned), a magical trunk, a foe glass (now broken and in the Room of Requirement), a Sneakoscope, and a Secrecy Sensor. At various times he had access to the Marauder's Map and Dumbledore's Put-Outer.

Possible name meanings
"Alastor" = English from Greek, an avenger or nemesis; the implication is that of terrifying but just retribution.
"moody" = describes someone whose outlook or personality changes quite often, usually in a negative way. Alastor Moody certainly fits that description. The word also has an alternate meaning of 'counterfeit' or 'false' [NSOED].

Profile
Retired Auror, considered one of the best Dark Wizard catchers the Ministry has ever had. Moody came on staff for a year at Hogwarts, but  spent it at the bottom of a magical trunk, unbeknownst to anyone but the imposter who put him there (GF). Moody is a member of the Order of the Phoenix.

Mad-Eye is noted for his paranoia, particularly in regard to food and drink, but also wand safety; this last may be related to his own missing leg (GF, OP3), but that is mere speculation. Moody takes command of any operation he’s associated with. He’s brusque and efficient and anticipates the moves of the Death Eaters.

He organized the rescue of Harry Potter from Privet Drive for the last time at the end of July, 1997, but was killed in the ensuing battle (DH4, 5). His body was never recovered. However, Harry Potter later discovered his magical eye affixed to Dolores Umbridge’s office door and took it. He buried the eye under a tree in a nameless forest (DH15). Moody’s favorite expression was “Constant vigilance!”

MOODY in the MOVIES
The role of Moody (and Crouch as Moody) is played by Brendan Gleeson (IMDB).