He was the creator of the comic strip 'Garth', which I used to read many, many, years ago, but is more famous as the creator of 'Modesty Blaise'. She first appeared in a comic strip; it was superb (approximately 4.7 billion times better than Joss Whedon's incoherent drivel, and original artist Jim Holdaway and his successor Enrique Romero were as far above Georges Jeanty as Michaelangelo was above a blind cave-dwelling neotonous gilled amphibian) but it was when he started writing the stories as novels that he reached his greatest heights.
The first novel was initially written as the script for a movie. The finished film used only one line from O'Donnell's script and it was... utterly abysmal. The novel, however, was sublime. A masterpiece of the spy caper genre - far outclassing the Bond novels. Alas the dire movie tarnished Modesty's image and, although the novels did sell millions, they failed to achieve recognition as the matchless works of genius that they were.
Towards the end of the novel series they deteriorated a little, and the villains became slightly too similar, but even the weakest of them is better than the best of any other thriller writer (except possibly Gavin Lyall at his absolute peak).
It's probably my heroine-worship of Modesty that has led me to specialise in writing stories with strong female central characters. I know none of my creations can ever match her but, if you shoot at the stars, you'll still reach a decent height even if you fall short.
Rest in piece Peter O'Donnell; if there is a Heaven I hope you are there with Modesty and Willie, Sir Gerald, Jack Fraser, Weng, Steven and Dinah Collier, Lucifer, Lady Janet, and Little Krell.