The mystery of an ancient Hindu-Buddhist kingdom in Malay Peninsula

One of the joys of travelling across South East Asia is to discover vast temple complexes – much bigger than the biggest temples in south India – which are clearly and heavily influenced by Indian architecture. For example, the sprawling Angkor Vat in Cambodia and the massive temple complexes in Borobodur and Prambhanan in Bali, Indonesia. Now, this piece in Scroll explains that rulers of Indian descent were also dominant in the Malay Peninsula and built a massive kingdom in what is modern day Thailand and Malaysia:
“….peninsular Malaysia has modest archaeological remains of great kingdoms of yore. But there is still a place where that past can be found: literature. The Kedah Annals, a Malay literary work that gives a romantic account of the history of the Malay kingdom of Kedah, mentions the Langkasuka Hindu-Buddhist kingdom which is believed to have been founded between the first and third century.
“Langkasuka, according to the Kedah Annals, was the name by which the ancient settlement by the Kedah Peak in Kedah was known,” WA Linehan, an English civil servant and scholar, wrote in the April 1948 edition of the Journal of the Malayan Branch of the Royal Asiatic Society. Kedah at that time was home to settlements of traders from India. Historians suggest the kingdom was located near Pattani, which is now in southern Thailand, and at its peak, it likely covered a vast area in modern-day Malaysia and Thailand.”
Fascinatingly, if you read the piece in the Scroll, you will discover that no one has been able to figure out who exactly built this massive kingdom. Was it a local warrior who travelled to India, learned Indian customs and methods of war and then returned home to conquer or was it an Indian warrior who sailed off to Thailand-Malaysia and founded a clan which ruled for centuries?