The Mtho btsun should be Sanskrit Udbhaṭa, but the last part of the name is quite problematic (perhaps an Indic form *Coyaga??).
Bu ston's History (1989), Catalogue Section, p. 407.7: slob dpon tho btsun tso yag gis mdzad pa'i gsang sngags kyi tshul gyi snang ba rin chen bzang po'i 'gyur.
Bibliography:
Mantranayāloka (Gsang sngags kyi tshul gyi snang ba). Tôh. no. 3710. Dergé Tanjur, vol. TSU, folios 76r.4-78v.6. Tr. by Padmākaravarman and Rin chen bzang po.
Dergé colophon: gsang sngags kyi tshul snang ba zhes bya ba / rdo rje slob dpon chen po mtho btsun btso yags kyi zhal snga nas mdzad pa rdzogs so // // rgya gar gyi mkhan po padmā ka ra warma dang / zhu chen gyi lo tsā ba dge slong rin chen bzang pos bsgyur cing zhus te gtan la phab pa.
