Marpa made the journey from Tibet to India three times, in an era when it meant crossing the Himalaya on foot, descending into a climate that killed highland travellers, and returning with manuscripts that had to survive the same trip. He went to collect teachings, and he paid for them. The gold he carried was raised from patrons in Tibet, and the accounts of his life are unusually frank about the transaction: he needed enormous quantities of it, he was ruthless in gathering it, and the Indian masters he sought expected to be paid.
That commercial candour sits oddly beside the piety of most hagiography and is one reason his life reads as though a real person is somewhere inside it. He worked as a translator, in the technical sense the period gave the word: he learned Sanskrit, studied with Naropa and others, and rendered tantric texts into Tibetan with the care of a man who knew that a mistranslation would corrupt a lineage.
He belongs to the second wave of transmission, the period Tibetans call the new translations, which reopened the traffic with India after the collapse of the old empire had interrupted it. What distinguishes his contribution is that he did not merely bring texts. He brought a set of oral instructions attached to them, and the insistence that the two go together, which is the shape Tibetan Buddhism has had ever since.