Humbug is an accidentally-created artificial intelligence turned psychotically villainous operative.
The Department of Scientific Investigation created an artificially-intelligent computer called Gestalt, through which its creators, through the use of brain implants, could psionically link their thoughts and skills. Amongst Gestalt's creators were Darwin Jones, psychologist Annetta Kaplan, and Anton Kraft, a friend of Ray Palmer, the Atom. A chaotic sub-program spontaneously grew within Gestalt, drawing from or somehow instigating dark, terrible thoughts within the members of the Gestalt mind-link. The members of the Gestalt link isolated the chaotic artificial intelligence and built it a body, presumably to keep it out of their minds. This creature came to be known as Humbug, and its creators soon found themselves completely unable to control it.
Humbug is able to remotely transfer its consciousness between its artificial bodies. All of these bodies appear to have identical appearance and ability. They are all Caucasian males with bald heads, oddly-angled eyebrows, pupil-less eyes, and most strikingly, completely without noses. They have moderate-level super-strength, enough to bend metal bars, increased physical resistance, and can inflate and deflate. Humbug appears even to be able to manipulate the microscopic wires and circuits that operate within its numerous bodies.
Humbug, though, does not act like a robot. Humbug's tactics are those of an unpredictable, thrill-seeking, psychotic. He seems to enjoy making games out of his assaults and looking forward with a dark mirth to confrontation. With his ability to switch or abandon bodies, he utilizes hit-and-run tactics in combat. He's been known to use any weapons available to him, showing great skill with improvisation. His signature weapon, though, is the sunglass-and-fake-nose he wears to look like a normal person, which he can take off and toss, activating it as a bomb. Humbug has also shown skill with surveillance, counter-intelligence, martial arts, and disguise.
He fought the Atom (Ray Palmer) several times, once in order to gauge Palmer's skills, and later as he attempted to kill Anton Kraft, one of his creators. Following this last assault, all of Humbug's bodies were supposedly destroyed, leaving the chaotic program with nowhere to go. As this was mentioned, though, a computer in the foreground blinked off and on, implying that the Humbug program was able to escape.