Spyal Lo tsā ba in Grub chen o rgyan pa'i rnam par thar pa byin brlabs kyi chu rgyun, "A biography of the famed Tibetan Mahāsiddha O rgyan pa Seng ge dpal by Zla ba seng ge," Sherab Gyaltsen Lama (Gangtok 1976), p. 8.
He was one of the four main disciples of Mar pa, and initiator of the Mes lineage. See Blue Annals, pp. 73 (Mes tshon po Dpyal Se tsa), 405-406 (here he has the name Mes tshon pa Bsod nams rgyal mtshan, or simply Mes tshon po).
Note the name Se rtsa Bsod nams rgyal mtshan (q.v.) that occurs in several Tanjur colophon.