The figure on the right might be indentified as Gayadhara, an Indian master who brought the teachings of Buddhism to Tibet in the early 11th Century; compare a later portrait in W. Zwalf (ed.), Buddhism, Art and Faith, 1985, cat. no. 195.
Portraits of this type are based on the emergence of Arhat portraits in the 15th century derived from Chinese prototypes of the late Yuan and early Ming dynasties. A single figure is thereby harmoniously embedded in a landscape setting; cf. M. Rhie and R. Thurman, Worlds of Transformation, 1999, fig. 16, for a comparable landscape setting in a palette of green and blue in an Arhat painting dated Yongle in the collection of the Brooklyn Museum, and from the Rubin Collection, ibid., cat. no. 26, after a 15th century composition; two further portraits in P. Pal, Tibetan Paintings, 1984, pl. 73 and 74; and and from the Rubin Collection, M. Rhie and R. Thurman, Worlds of Transformation, 1999, cat. nos. 21 and 26.