[2] After graduating from Erlangen University in physics and chemistry, he conducted an 18-year experiment on Kabakon island, living a natural life on coconuts.

From this he developed an interest in health, issues that were being promoted by the lifestyle reform movement, which included writers such as Gustav Schlickeysen, author of Obst und Brod: eine wissenschaftliche Diätetik (Fruit And Bread: A Scientific Diet) in 1877.

[7] In the fall of 1899, Engelhardt joined the Jungborn ("Fountain of Youth") in the Harz mountains, Eckental, an association for wild living, which was founded by brothers Adolf Just and Rudolf Just and whose basic principles were vegetarianism and nudism.

There he preached his idea that humans might live best in a "natural state" eating only coconuts, and gave public lectures in Leipzig and Nuremberg, where he was ridiculed.

[8] After serving for one year in the 14th Infantry Regiment, with a substantial inheritance, the 26-year-old took a trip on board the mail steamer Empire in July 1902.

He obtained on 2 October 1902, from Queen Emma Kolbe's Forsayth Company, a coconut and banana plantation of 75 hectares on the coral island of Kaka Kon (Kabakon) for 41,000 marks.

On Kabakon, as the only white man among 40 Melanesians, he built a three-room hut and began implementing his ideas of living close to nature.

This view, called cocoivorism, culminated in Engelhardt's statement that the constant consumption of coconuts leads man to immortality.

He held that man was a tropical animal, not intended to live in caves called houses, but to wander, as Adam did, with the sun beating upon him all day and the dews of heaven for a mantle at night.

Living such a life, he believed that the healing and curative powers of the sun would in time render a man so immune that sickness could be overcome".

Although he had brought 1200 books with him, Engelhardt felt isolated and wanted a community of like-minded people, an "Order of the sun", for which he wrote promotional literature published in Europe.

In 1903, the first newcomers arrived on the island, including nature writer August von Bethmann-Alsleben (born 21 April 1864), from Heligoland,[11] with whom Engelhardt wrote his main book The Carefree Future (1898).

According to the New Zealand Herald: "The long-haired, naked vegetarians, thought to number no more than 30, were a stark contrast to Kaiser Wilhelm's rigid turn-of-the-century Germany – and modern-day perceptions of German colonisers in the Pacific as military men, traders or administrators.

He told a German civil servant of the government, that by June 1906 he would leave on the next available steamer for Germany, but died, possibly of malaria, in September 1906.

[3] He only attended to his plantation, but the coconut apostle became a point of interest for tourists in German New Guinea including painter Emil Nolde.

He announced he wanted to establish an "international tropical colonial empire of frugivores" for nudism and sun-worship, which should include the entire Pacific, South America, Southeast Asia and Central Africa.

His plantation operated since 1909 as Engelhardt & Company and was farmed by manager Wilhelm Bradtke, a vegetarian who had arrived in Kabakon in March 1905.

Writing in a vegetarian magazine in 1906, Bradtke documented Engelhardt's major leg wounds, gout in the fingers, skin rashes, fever and seizures.

An admission fee of 3,000 marks had been imposed to prospective members of the colony by Wilhelm Bradtke, causing a shortage of newcomers.

In 1914, Engelhardt received a letter from Benedict Lust, leader of an American society of vegetarians about possible migration, but World War One stopped their plans.

Engelhardt continued to study the indigenous medicinal plants and homeopathy, and sent a lot of specimens to the botanic gardens of Brisbane and Sydney.

He was buried in Inabui Cemetery on Mioko, Duke of York islands, but there is no burial site, which was possibly destroyed in World War Two.

He wrought himself up to a great frenzy, fell upon the deck and was restrained only with difficulty from flinging himself overboard and swimming back to the island.

"[3] According to The New York Times, "Wrapped in a German flag, Engelhardt, founder and survivor of the sun worshippers, was laid to rest beside Lutzow and Eukens on the beach at Kahakua (Kabakon)".

[15] Engelhardt appears as a major character in Adrian McKinty's 2014 novel The Sun Is God (ISBN 1616140682), whose plot revolves around real life suspicious deaths at the colony.