In Biggles Hits the Trail, Ho Ling Feng was the leader of the Chungs, an ancient race of people who controlled the Mountain of Light, located somewhere in the Himalayas in Western China on the border with Tibet. Under his leadership and that of his predecessors, the Chungs had harnessed the radium in the mountain and developed a number of powerful technologies, including a means to make the Chungs invisible and a powerful ray weapon which could paralysed enemies. With these advantages, Ho Ling Feng planned to take over the world until his plans.
When Biggles and friends came to explore the Mountain of Light, Ling Feng at first gained an important advantage by capturing Dickpa and Malty. However when Biggles later wounded and captured Ling Feng's son, Prince Sing Hi, the Chung ruler was forced to release the prisoners in exchange for his son. With his friends freed, Biggles was able to focus his attention on thwarting the Chung plan to attack the world, an effort at which he ultimately succeeded.
Nothing much is said about Ling Feng in the book other than being styled "His Highness" and dressed in purple robes. While his age is not stated, he is likely to have been extremely old as one of the properties of the radium in the mountain appeared to be to grant the inhabitants there extreme longevity. Angus McAllister, for example, did not age much in all of the fifty years he was held prisoner there. There is also a suggestion made at the conclusion of the book that Marshal Li Chen, the dictator of China, had financed Ho Ling Feng.