What is "sthiramati"

Sthiramati (Sanskrit; Chinese:安慧 Tibetan: blo gros brtan pa) or Sāramati was a 6th-century Indian Buddhist scholar-monk. He was based primarily in Valābhi (present-day Gujarat), although he is thought to have spent some time at Nālandā. He was renowned for his numerous and detailed commentaries on Yogācāra and Abhidharma, works by Vasubandhu and others, as well as for a commentary on the Kaśyāpa-parivarta.

Takasaki is certain that the author of the embedded commentary (verse and prose) to the core text (verse) of the Ratnagotravibhāga [RGV version as per Johnston] is Sāramati through his analysis of the RGV with the Dharmadhātvaviśeṣaśāstra.