Its action is in what is called the first spread of Buddhism in Tibet (since after a period of decline, Buddhism experience a second broadcast from the 11th century).
Padmasambhava (the "lotus born") is said to have helped build the monastery of Samye, in competition with Shantarakshita, the very one who had asked his colleague to come yogi help promote Buddhism in Tibet (and while Shantarakshita represented Buddhism in his philosophical approach (unifying the teachings of Nagarjuna, Asanga and Dharmakirti), while Padmasambhava represented the yogic approach and magical-mystical Buddhism).
To paraphrase Philippe Cornu, Padmasambhva is important more for its place in the collective imagination of Himalayan Buddhism for its real historical role, it seems to have been actually very modest, so much so that it is not established that he would have personally witnessed the construction of the Samye monastery.
His spiritual influence is considerable, however, since, considered to have hidden spiritual treasures, it is indirectly responsible for tertön, researchers of these treasures (terma). One example is of Dilgo Khyentse Rinpoche tertön comtemporain, which is said to have revealed some of the hidden texts by Padmasambhava.
It is true and I fixes that tantra had not disappeared in India when Padmasambhava introduced them in Tibet.
This man, semi-historical, semi-legendary, was born in Kashmir (or the current Pakistan), at a time when Buddhism was strongly influenced Shaivism of this region, and so had largely assimilated the esoteric teachings of this religion (visualiation deities in particular). It is therefore a Buddhist master very inspired by these teachings traveled to Tibet and who helped them impose a mystical way, whatever name you give it (Vajrayana Tantrayana, mantrayana ...). It is assumed that this type of education, mixing sutras and tantras, was adapted in Tibet and the Himalayan region, given the soil of local animist beliefs.
It was, in any case, Buddhism as practiced in neighboring areas of India in Tibet and one who had every chance to introduce and develop it there.
The spread of Buddhism has always followed the paths dedicated to trade between regions, pilgrims joining the merchant caravans, and it is logically matiné Buddhism Kashmir Shaivism that could reach into Tibet, more than that of Theravada, who had already moved to southern India (although it must be stressed that the Chinese Chan was also developed in Tibet, this gave rise later to a conflict and Lhasa council that lives, essentially, the Indian triumph at the expense of Mahayana Buddhism Chan).
This teaching was referring to the Indian deities, which were adopted by the Buddhist pantheon such as protective. Thus the terrifying Mahakala (protector of the four Tibetan schools) has its origins in India. His fierce appearance is due to its role of protecting the doctrine of his enemies, as well as a bodyguard to a department store must not have the nice, the guardian of education must by its one aspect repel heretics.
Padmasambhava is especially revered by the ancient Tibetan School (Nyingma) who made his main teacher. However, other schools also hold him in high esteem, and can be visited in Tibet, Bhutan, Ladakh among other caves in which the teacher is supposed to have stayed and meditated.
It is to him that we owe also the adoption by the Himalayan Buddhist pantheon of local Tibetan deities, he is said to have tamed to make other guardians of the doctrine.
With specific book by Philippe Cornu, it should be noted that it attaches one hand to the legendary story of Padmasambhava, who probably even less to do with the reality that for Buddha history. It is thus regrettable that spends no more developments in research on the historical Padmasambhava, it is true that significantly contradicts the legend or away a lot.
It evokes the other hand the history of Tibetan Nyingma school, one that considers Padmasambhava as its creator, this school is the only one that refers directly to the first spread of Buddhism in Tibet. It is thus a question of different masters of this school, again with regret that the most important place is made to the legend rather than history.
The book, however, an interesting introduction to both the history of the spread of Buddhism in Tibet that character Padmasambhava. My regret is that Philippe Cornu is not referred to the most exciting studies on this subject by Anne-Marie Blondeau, he was nevertheless the student.
For further reading a book (unfortunately sold out) who deals with high accuracy and multiple historical references in the history of Tibetan Buddhism:
RELIGIONS OF TIBET AND MONGOLIA.
And a second, recently reissued, written by a leading expert in the subject and contains long developments on the spread of Buddhism in Tibet:
Tibetan Civilization