Seub Nakhasathien (Thai: สืบ นาคะเสถียร, pronounced [sɯ̀ːp̚ nāː.kʰáʔ.sàʔ.tʰǐan],RTGS suep nakhasathian; 31 December 1949 – 1 September 1990) was a Thai conservationist, environmental activist, and scholar who is renowned for his effort to protect Cheow Lan Lake (Rajjaprabha Dam Reservoir), Thungyai Naresuan Wildlife Sanctuary, and Huai Kha Khaeng Wildlife Sanctuary.

In their home were pictures of his father as a young man with a dead tiger trophy and a pair of antelope horns.

He was not only a smart student, but he was also the best trumpet player at the school and an accomplished artist, drawing comic books for his friends to read.

Seub said that, at first, he did not want to study forestry--it was his fifth choice of major--but, when he got accepted, he told his mother that he should go, as he was not young anymore.

His classmate and fourth year roommate at university said that Seub was a brilliant student, always sitting at the front of the class, taking notes that he illustrated with drawings.

In 1979, he was awarded a British Council scholarship for a master's degree at London University to study resource and environmental conservation.

Seub conducted research on wild animals, especially birds, gorals, chamois, serows, and ecology at Huai Kha Khaeng and Thungyai Naresuan Wildlife Sanctuary.

The resulting flooding destroyed 185 square kilometres of the country's largest remaining area of lowland evergreen rain forest.

For the first time ever in Thailand a rescue operation was carried out to try to save some of the wildlife, which included threatened and endangered species stranded on islands as the waters rose.

[1] In 1988, Seub and his fellow conservationists took action against the Thai Plywood Co., Ltd., a state enterprise under the Ministry of Natural Resources and Environment over a logging concession in Huai Kha Khaeng Wildlife Sanctuary.

According to UNESCO,[4] Thung Yai-Huai Kha Khaeng Wildlife Sanctuary World Heritage property lies in Uthai Thani, Tak, and Kanchanaburi Provinces in the west of Thailand, along the border with Myanmar.

Thung Yai-Huai Kha Khaeng Wildlife Sanctuary encompasses two important river systems, the Upper Khwae Yai and the Huai Khakhaeng.

The property, encompassing 622,200 hectares, is the largest conservation area in Mainland Southeast Asia and is one of Thailand's least accessible and least disturbed forest areas.Seub's vision was to solve the problems of the Huai Kha Khaeng.

He, in turn, asked his campaigning colleague, Belinda Stewart-Cox, to help prepare the nomination since it had to be in English and he was too busy to focus on such a major undertaking.

In mid–December 1991, approximately a year and a half after Seub's death, UNESCO certified Thungyai Naresuan-Huai Kha Khaeng Wildlife Sanctuary as a World Heritage Site, the first of its kind in mainland Southeast Asia.

[4] In 1989, under pressure from many sides while he was working as head of the Huai Kha Khaeng Sanctuary, dealing with multiple problems including the non-payment of worker's wages, disagreements with higher-ups, the death of some employees at the hands of encroachers, Seub became despondent.