Douglas Keen presided as editorial director and creative force over Ladybird Books. One of the greatest postwar successes in British publishing, the series was a valuable aid to children in learning to read and informed them on every aspect of life in a simple and pleasing format of words and colour illustrations contained in a pocket-sized hardback.

From the 1950s onwards there could hardly have been a household or school in the country that did not have one or more of the distinctive 24-page Ladybird books on their shelves. Their price remained at 2/6d (12½p) for more than 20 years, well within pocket-money range.

Their subjects ranged from heraldry, the lives of the saints, the farm and garden flowers to Pharoahs and mummies, telling the time, the weather and space. There were also retellings of fairytales, nursery stories, ancient myths and the lives of historical figures as well as simplified versions of classic novels. Nothing and no one was left undiscovered, whether it was what to look for in summer or Joshua and the Battle of Jericho.

And the whole enterprise came about almost by accident. The company that Keen joined, aged 23, in 1936, Wills & Hepworth of Loughborough, Leicestershire, was not a publisher but a commercial colour printer producing catalogues and technical literature for the Austin and Rover motor car companies and BSA motorcycles. But there were slack times when the company wanted to keep the machines running and the workers occupied and so turned to printing the very first Ladybird books in a large format on cheap paper in two colours which were sold to market hucksters at no great profit.

Keen was called up in 1940 and served in the RAF, but was paid a small retainer on the understanding that he would return after the war. When he did so, in 1946, he was put in charge of the books, little more than a sideline, with a brief to try to make them more profitable. Conscientiously, he set out to research the market, visiting bookshops and schools in Manchester, Edinburgh, Leeds and Liverpool. Schools were changing. Books were no longer kept out of reach in glass cabinets but were being placed in classroom book corners where they could be read at will.

He soon realised that what the Ladybird books needed was a smaller format, better-quality paper and far more research. The result was The Book of British Birds and Their Nests to be written and illustrated by specialists in their field. It quickly sold out and there was a second print run of 50,000 copies. Encouraged by its success and bursting with enthusiasm, Keen began making plans not just for individual titles but for whole series.

Nature was clearly popular. Another was The Story of . . . series: Captain Cook, Peter the Fisherman, the Cowboy, Dick Whittington. There were more nature books, employing the talents of distinguished wildlife artists such as C. F. Tunnicliffe, Rowland Hilder and John Leigh-Pemberton. Research was conducted into every new title to assess its potential sales. As a reassurance to teachers, educationists were engaged to write books for the very young such as an ABC and Shopping with Mother.

By now Keen’s ambition knew no bounds and he hit upon the idea of a Ladybird reading scheme after reading an article in The Teacher by William Murray about the key words to literacy. Murray was hesitant about supplying the text, but after being shown some specimen spreads illustrated by Harry Wingfield, a commercial artist and an old friend of Keen, he agreed to write for a series to be called the Ladybird Key Words Reading Scheme and featuring Peter and Jane. There were 36 books, three at each of the 12 reading stages, and all published simultaneously and stockpiled for the launch date. It was a financial gamble.

“At one point the head printer in the litho room came up to me looking very worried because he wasn’t used to having so much stock there,” Keen recalled. “He had thought the books weren’t selling and their jobs were at risk.” But the books were an immediate success and in 1957 Keen was invited to join the board as editorial director.

He was now responsible for commissioning and managing the authors and illustrators. They had to be specialists in their field and, of course, they had to be able to simplify the complex and make it attractive to children. Keen turned to some of the finest artists of the day, who were working on The Eagle, the popular boys’ comic which carried many factual series, and employed Robert Ayton, Martin Aitchison, Frank Hampson, then struggling to make ends meet but who became celebrated for his Dan Dare strip, and Frank Humphris, who was an expert on the American West. The People at Work series was illustrated by John Berry, who was also a portrait painter, and the Junior Science series was decorated by Harry Wingfield, whose illustrations of children were particularly sympathetic. Keen insisted on accuracy as all important. Readers were only too ready to write in to Ladybird Books if they ever found a mistake. The illustrators tended to become his friends for life, not least because Keen was punctilious about prompt payment.

Among the How it Works series was a book on The Computer which led to much merriment in the media when it was discovered that the Ministry of Defence, which was introducing its staff to computers in the late 1970s, had asked Ladybird to produce 100 copies or so in plain covers so that civil servants were not made to feel childlike. The nation’s children, it seemed, were better informed than its adults.

The same discreet approach was adopted for The Motor Car when Thames Valley Police began switching officers on the beat into patrol cars.

Douglas Keen was born into a working-class family in Cheltenham in 1913. His father, a market gardener, left the family home when Keen was a boy, and his mother made a living by tailoring and hat-making. Keen won a scholarship to the local Pate’s Grammar School, after which he studied art and marketing at evening classes.

During the Second World War he served in Belgium and France with a mobile radar unit before rejoining Wills & Hepworth where he spent the next 28 years building Ladybird Books into a publishing phenomenon. By the 1960s the imprint was so successful, producing hundreds of titles, that the board decided to abandon the printing of catalogues.

Ladybird became a household name and by 1971 it was selling some 20 million copies a year. Seeing the potential for export it also produced books in foreign languages. Even at the peak of its success the business’s editorial department continued to be run from an extension at the back of Keen’s house in Stratford-on-Avon. Then in 1973 the privately run company was made an offer it could not refuse — £3.37 million — and sold Ladybird to the Pearson Longman Group.

Keen was a gentle, shy man with an abiding hunger for knowledge and an ardent desire to introduce the young to the joy of learning.

His wife, Margaret, who was a great help to him in his work, died in 1999. He is survived by their two daughters.

Douglas Keen, publisher, was born October 27, 1913. He died on November 6, 2008, aged 95