In September, 1931, the Irving family - James, Margaret and daughter Voirrey (13) - claimed to hear persistent scratching and rustling noises behind their farmhouse's wooden wall panels. At first they thought it was a rat, but then the unseen creature began making different sounds, sometimes spitting like a ferret, or growling like a dog, or gurgling like a baby. The creature soon revealed an ability to speak, and introduced itself as Gef, a mongoose. It claimed to have been born in New Delhi, India, in 1852. According to Voirrey, who was the only person to see him properly, Gef was the size of a small rat, with yellowish fur and a large bushy tail (the Indian mongoose is in reality much larger than a rat and does not have a bushy tail).

Gef variously claimed to be "an extra extra clever mongoose", an "earthbound spirit" and "a ghost in the form of a weasel". He once said, "I am a freak. I have hands and I have feet, and if you saw me you'd faint, you'd be petrified, mummified, turned into stone or a pillar of salt!" Voirrey Irving, who took Gef under her wing, died in 2005. In an interview published late in life, she maintained that Gef was not her creation.