There are two types of people: those who rejoice that Russell Hoban’s first eight novels for adults have just been reissued as Penguin Modern Classics; and those who will rejoice once they’ve read them for the first time.

The Pennsylvania-born Hoban lived and worked in England, publishing his first novel in 1973, aged 48. He died in 2011. Best known at first as writer of children’s fiction, then for his post-apocalyptic novel Riddley Walker (1980), he once referred to his fans as a “bunch of charming weirdos”, which is a fitting description of his books too. Artworks by Eduardo Paolozzi used for the covers of these editions capture Hoban’s colourful eccentricity.

Each book is surprising – featuring spacemen, map-makers, castrated Jews – but you also know what you’re getting, which is curiosity, wonder and a world-encompassing empathy; books that “might get you to those places in your head that you can’t get to on your own”. His stories don’t take themselves seriously, but have big ideas and such a wide range of reference – artworks as the home of the human soul always feature – that they benefit from being read with a search tab open.

Hoban’s third novel, Turtle Diary (1975), is about two lonely middle-aged Londoners, Neaera and William, who narrate in alternating chapters, unconnected except by a mutual desire to free the turtles from London Zoo. Whether they free them or not isn’t the point; there’s a love story too, but not the expected one. The story is really about connecting people, and finding a place in the world for yourself, particularly if you agree with Neaera that “more and more I think that madness is the world’s natural state and to expect anything else is madness compounded”.

But making positive gestures – releasing turtles, finding out, carrying on – even in the face of that madness – is the point. Little wonder that one cover review calls Turtle Diary “life-saving”, or that Max Porter said that it “has medicinal qualities. I only need to think about it and I’m in a better mood.”

Mr Rinyo-Clacton’s Offer (1998) adopts a similar refusal to fit. (“Crazy? The word is meaningless, read the papers and tell me we live in a sane world”), but to both darker and funnier ends. Here are two men: one knows why he’s unhappy and the other doesn’t. The second, the sinister Mr Rinyo-Clacton, offers to “buy the death” of the first man, Jonathan Fitch: he’ll give him £1m and let him live for a year; then it’s lights out. “Mmmmmm, yes! Dark pleasure! Secret joy!”

Mr Rinyo-Clacton is someone who alters the world to make it fit him. Jonathan believes he has nothing to live for since his partner, Serafina, left, so accepts the offer, finding of course that life is more valuable when it’s running out. Hoban’s wide-eyed vision helps, suffused with a love of London only possible for an immigrant still beguiled by his adopted home, from tube journeys (“through the London clay beneath the surface of things”) to railway stations: “Charing Cross, all agleam with its swaggering arches, urged action. Live! it said. Go! Do!”

But it’s The Medusa Frequency (1987) that Hoban said held the key to his writing. You can see why, as it contains elements familiar from many of his books: a narrator who’s a writer; names that sound vaguely punny (Herman Orff, Istvan Fallok); a culturally omnivorous interest in art (here, Vermeer’s Girl With a Pearl Earring); and, always, empathy for “the general straggler and struggler, the person for whom the whole sweep of consciousness is often too much”.

This is Hoban’s loosest, most anarchic novel, broadly about making a film of Orpheus and Eurydice, but where a line such as “The head of Orpheus turned up as half a grapefruit and in an absent-minded moment I ate it” can seem quite normal. This whimsy forms a template for Hoban’s later books – he wrote eight more, not reissued in this series – which mingled many of the elements in these early titles (esoterica, technology, love at first sight) to likable but diminishing effect. The Medusa Frequency is a vision of the future: soon all of Russell Hoban novels would be like this.

• Turtle Diary by Russell Hoban is published by Penguin Modern Classics (£9.99). To order a copy go to guardianbookshop.com. Delivery charges may apply

• Mr Rinyo-Clacton’s Offer by Russell Hoban is published by Penguin Modern Classics (£9.99). To order a copy go to guardianbookshop.com. Delivery charges may apply

• The Medusa Frequency by Russell Hoban is published by Penguin Modern Classics (£9.99). To order a copy go to guardianbookshop.com. Delivery charges may apply