The story revolves around Kenzo Tenma, a Japanese surgeon living in Düsseldorf, Germany whose life enters turmoil after he gets himself involved with Johan Liebert, one of his former patients, who is revealed to be a psychopathic serial killer.

Urasawa later wrote and illustrated the novel Another Monster, a story detailing the events of the manga from an investigative reporter's point of view, which was published in 2002.

Dr. Kenzo Tenma is a young Japanese brain surgeon, working at Eisler Memorial Hospital in Düsseldorf, West Germany.

Tenma eventually learns the origins of this "monster": from the former East Germany's attempt to use a secret orphanage known as "511 Kinderheim" to create perfect soldiers through psychological reprogramming, to the author of children's books used in a eugenics experiment in the former Czechoslovakia.

Tenma learns the scope of the atrocities committed by this "monster", and vows to fix the mistake he made by ending Johan's life.

The calm surface of the music giving way to darker undercurrents, signifying the conscience of the lead protagonist and the themes of morality, fate, resignation, and free will.

[15] The credit sequence features illustrations from the book Obluda, Která Nemá Své Jméno (The Monster Who Didn't Have A Name) by Emil Scherbe which was published by Shogakukan on 30 September 2008.

The show aired on Syfy's Ani-Mondays with two episodes back-to-back each Monday night at 11:00 pm EST, beginning 12 October 2009, as well as on its sister network Chiller.

However, due to low sales of the first box set, Viz decided not to continue releasing the remaining episodes on DVD and later dropped the license.

[25] In 2013, it was revealed that Guillermo del Toro and American premium television network HBO were collaborating on a pilot for a live-action TV series based on Monster.

[41] Writing for Time, Pulitzer Prize for Fiction winner Junot Díaz praised the manga, proclaiming "Urasawa is a national treasure in Japan, and if you ain't afraid of picture books, you'll see why".

[42] About.com's Deb Aoki called Monster a multi-layered suspense series and satisfying mystery that stands up to repeat readings, although it is sometimes a "little hard to follow".

"[45] Kimlinger deemed the art "invisible perfection," never "showy or superfluous," with panels laid out so well that it is easy to forget how much effort is put into each and every page.

"[44] UK Anime Network gave the first volume a perfect score based on the engrossing story, but felt the artwork, while appealing, was not "groundbreaking".

Sparrow of IGN described Monster as a "Hitchcock film set to manga" and felt its real strength comes from its huge cast of interesting characters, who each have "a unique story and history to relate".

[49] Carlo Santos, also for Anime News Network, called Monster "a one-of-a-kind thriller" and suggests that one of the most overlooked qualities of it is that "amidst all the mystery and horror, there are moments of love and hope and all the good things about humanity.

"[51] Brienza noted that "there is nothing satisfactory ever revealed to fully account for [Johan's] supremely scrambled psyche," but concluded that as long as the reader does not look for "deep meanings or think too hard about whether or not it all makes sense in the end" they will enjoy it.

[55] Carl Kimlinger enthused that "It cannot be overstated how brilliantly apart from the anime mainstream this unsettling, fiercely intelligent, and ultimately uncategorizable journey into darkness is.

"[56] He praised Madhouse's animation for not only keeping up the dark "cinematic quality of Urasawa's art" but also improving on it, as well as Kuniaki Haishima's score for adding "immeasurably to the series' hair-raising atmosphere.

"[57] Though he noted Viz Media's inability to acquire the original ending theme song due to licensing problems, Kimlinger also called their English dub of the series one of the best in recent memory.

[57] Kimlinger praised the series, for "its fidelity to Naoki Urasawa's original manga", commenting that "there isn't a scene left out, only a handful added in, and as far as I can tell not a line of dialogue changed or omitted.