The most famous early teacher was Padmasambhava, also known as Guru Rimpoche, who arrived in the 8th century CE.
In later history, he was said to be a manifestation of the cosmic Buddha known as Amitabha (the ruler of the famous Pure Land known as Sukhavati), who appeared to discoverers of ancient Buddhist texts.
Those discoverers of texts, who were known as “tertons,” were considered to be incarnations of Padmasambhava’s own disciples in later lifetimes.