As you know, the historical Buddha is usually called Shakyamuni in the Mahayana Sutras and by Mahayana practitioners.
In the old Pali Dictionary Abhidhanappadipika we can find 39 names and titles of the Buddha. Sakyamuni is one of those. These 39 names and titles occur in the Pali texts - some of them are common, as Bhagava, Buddha, Gotama, Sugata and a few others, others (as for instance Sakyamuni) occur only in a few cases.
This is not at all meant as a criticism of the Mahayana. I am just curious: Does anyone know why just the title Shakyamuni gained so much terrain in the Mahayana?


