Steve Ditko, who has died aged 90, was the artist who brought Spider-Man and Doctor Strange to life, one of the three crucial creators of the Marvel explosion that redefined comic books in the 1960s. The trio – Ditko, the writer Stan Lee and the artist Jack Kirby – created and refined the iconic characters who moved from featuring in 12-cent comics to dominating film screens in productions costing hundreds of millions of dollars.

Like Kirby’s, Ditko’s work was stylised, but where Kirby’s square-jawed characters’ power exploded through the panels, Ditko’s characters stretched through them, their faces almost cartoonishly expressive. He was the perfect artist to combine the grace of Spider-Man with the nerdish insecurity of his alter ego, the teenager Peter Parker.

Spider-Man was Lee’s idea and he first gave it to Kirby to develop. Unhappy with the result, he passed it on to Ditko, who came up with the costume, powers and back-story. He was an immediate hit when he debuted in Amazing Fantasy 15 in 1962. Marvel stories were all produced in much the same manner. The writer, in the early days almost always Lee, provided the artist with a plot line, sometimes just an idea, which the artist turned into a story. Lee then added dialogue to the finished panel art.

Shortly into the Spider-Man series, Ditko would receive additional credit as “plotter”, and eventually Lee was willing to cede “co-creator” status to Ditko, including in the credits of the Spider-Man films. There are reports of Ditko having received royalties from the films, but if so the amounts were not large.

Doctor Strange came along the following year. Ditko’s conception of Stephen Strange, the surgeon whose hands are crippled in a car crash, and who, seeking a cure, becomes “the Master of the Mystic Arts”, led to a character whose greatest battles were fought on a spiritual plane while his human body reposed back in our world. Villains were mind-bending, such as the Dread Dormammu, whose head and hands were flames, or Eternity, whose silhouette figure encompassed all universes, and who starred in an unprecedented 17-issue story arc that culminated with Strange and Dormammu joining forces. The Marvel audience was expanding, and the hippy young of the 60s reading Doctor Strange felt Ditko must be one of them.

In reality, Ditko was anything but. He was born in Johnstown, Pennsylvania, where his father Stephen was a master carpenter at a steel mill and his mother Anna was a homemaker. His father loved newspaper comic strips, and Ditko’s early influences were Prince Valiant, Batman and Will Eisner’s The Spirit. After leaving school in 1945, Ditko enlisted in the army, where he served in occupied Germany, drawing comics for the army paper.

In 1950 he used the GI bill to enrol in the Cartoonists and Illustrators School (now the School of Visual Arts) in New York, where he studied under Jerry Robinson. Robinson had drawn Plastic-Man, whose flexible motion is apparent in Ditko’s drawing. Robinson also created Batman’s most famous villain The Joker, whose exaggerations are pure Ditko.

Robinson was committed to getting work for his students, and Ditko soon joined the (Joe) Simon and Kirby studio, primarily assisting Mort Meskin. His first story appeared in an obscure comic called Daring Love in 1954, at which point he started working for Charlton Comics, published in Derby, Connecticut, about 90 miles from New York, and in 1956 with Atlas, the precursor of Marvel run by Martin Goodman. Atlas comics were collections of strange mystery tales; Ditko’s expressive figures and Lee’s clever writing were soon giving their stories pride of place.

With the Marvel renaissance in full flower in 1966, Ditko produced one of the great sequences in comic art, for Spider-Man 33, The Final Chapter. With Spider-Man buried under heavy machinery and unable to save his Aunt May, Ditko’s panels grow smaller; then, as his will to live drives him, they grow larger again until the final full-page drawing in which he sets himself free.

But at his creative peak, Ditko abruptly left Marvel. The reasons may have included a creative battle over a storyline in which Lee wanted The Green Goblin to turn out to be Parker’s best friend’s father, while Ditko wanted him to be a random character; Lee’s instincts proved correct. That highlighted Lee and Ditko’s polar opposites of character, described by the comics writer Neil Gaiman as “swinging Stan and the impossibly uptight Ditko”. The liberal Lee was quick to spot trends and jump on them, while Ditko was already a libertarian follower of Ayn Rand’s Objectivism.

Ditko moved back to Charlton, where page rates were low but he was given more freedom. He revived older characters including the Blue Beetle, who had first appeared in the late 30s, and Captain Atom, which he and Charlton’s main scripter Joe Gill introduced in 1960. In 1967 Ditko created The Question, a newsman, Vic Sage, who dons a spray-on faceless mask and fights ruthlessly against crime, driven by the tenets of Objectivism. An even more extreme version of the character, called Mr A, convinced of a black and white world of good and evil, appeared in Witzend, the artist Wally Wood’s self-published magazine.

These characters were the inspiration for Rorschach in Alan Moore’s Watchmen; Moore’s character takes Ditko’s to their logical conclusion. Moore says he asked Ditko if he had seen Rorschach, to which Ditko replied: “Oh yes, he’s like Mr A, only insane.”

Ditko worked with the writer Archie Goodwin on stories for the black-and-white magazines Creepy and Eerie, which captured the flavour of classic EC comics. In 1968 he moved to Marvel’s great rival DC. His two major creations were Ditko at his obsessive peak: Hawk and Dove featured two “heroes” whose philosophies reflected the antiwar movement, with Ditko’s sympathies lying obviously with Hawk, while The Creeper, with his garish costume and hysterical laughter (a nod to The Joker, perhaps) might have been the weirdest superhero ever.

This marked the end of Ditko’s greatest mainstream success. In 1975 Goodman tried to start a new version of Atlas, for which Ditko and Goodwin created The Destructor, with Wood inking Ditko’s pencils, but it was short-lived. For the next two decades he worked for almost everyone in the business, including new independent publishers such as Pacific and Eclipse, but his most notable creation was probably the light-hearted Squirrel Girl, written by Will Murray, for Marvel in 1992.

Retiring from the industry in 1998, Ditko teamed up with Robin Snyder to publish new work and collections of his older material in small press editions. He also contributed essays to Snyder’s fanzine The Comics. Ditko was famously reclusive. In 2007, Jonathan Ross attempted to track him down for the TV documentary In Search of Steve Ditko for BBC Four. It climaxed with Ross and Gaiman getting 25 minutes, off camera, with Ditko in his office. But Ross would not tell his TV audience what they discussed. “If you don’t like that, tough,” he said.

Ditko was found dead in his flat in New York on 29 June, having suffered a heart attack at some time in the previous two days.

• Stephen John Ditko, artist, born 2 November 1927; died c29 June 2018

• This article was amended on 10 July 2018. Squirrel Girl was created for Marvel rather than DC.