Answer by taking a quote from the following article:

Dr. Victor Von Doom (commonly known as Doctor Doom, or simply Doom) is a fictional character appearing in American comic books published by Marvel Comics. The son of a Romani witch, Von Doom has been depicted as a supervillain, the archenemy of the Fantastic Four, and the leader of the fictional nation called Latveria. While his chief opponents have been the Fantastic Four, he has also come into conflict with Spider-Man, Iron Man, Black Panther, and multiple others. Von Doom has also been depicted as a superhero, being the third character to take up the mantle of Iron Man and joining the Avengers.

Rapper MF DOOM bases his persona on Victor von Doom.  In the book Superhero: The Secret Origin of a Genre, Peter Coogan writes that Doom's original appearance was representative of a change in the portrayal of "mad scientists" to full-fledged villains, often with upgraded powers. These supervillains are genre-crossing villains who exist in adventures "in a world in which the ordinary laws of nature are slightly suspended"; characters such as Professor Moriarty, Count Dracula, Auric Goldfinger, Hannibal Lecter, Joker, Lex Luthor, and Darth Vader, also fit this description. Sanderson also found traces of William Shakespeare's characters Richard III and Iago in Doom; all of them "are descended from the 'vice' figure of medieval drama", who address the audience in monologues detailing their thoughts and ambitions.  Described as "iconic", Doom is one of the most well-received characters of the Marvel Universe, as well as one of the most recurring; in his constant battles with other heroes and other villains, Doctor Doom has appeared more times than any other character. The comics site Panels of Awesome ranked Doctor Doom as the number one villain in their listing of the top ten villains in comics; Wizard Magazine went a step further by declaring Doctor Doom the fourth greatest villain of all time.  Comic Book Resources ranks Victor von Doom as their fourth favorite Marvel character. Journalist Brent Ecenbarger cited him being able to "stand up against entities like Mephisto, the Beyonder, and Galactus and often comes out on top", as well as the tragedy of any "other number of circumstances could have led to Doctor Doom being a savior, but as it is, instead he remains Marvel's greatest villain.", a fact that later led to the character's redemption. Fellow journalist Jason Stanhope called his "master[ing] of sorcery and technology an unusual combination", and also felt "his inner sense of nobility sets him apart from lesser villains, in a similar manner to Magneto." Von Doom has also been favorably regarded by those who wrote for the character; Stan Lee declared Doom his favorite villain, saying that Doom "could come to the United States and he could do almost anything, and we could not arrest him because he has diplomatic immunity. Also, he wants to rule the world and if you think about it, wanting to rule the world is not a crime.", that Doom technically isn't a villain. Mark Waid echoed Lee's assessment of the character, stating that Doom "[has] got a great look, a great visual design [and] a dynamite origin."  A ride called Doctor Doom's Fearfall is located at Islands of Adventure in the Universal Orlando Resort.

What did others say or think about him?
Wizard Magazine went a step further by declaring Doctor Doom the fourth greatest villain of all time.