What does "Mundele Ndom" mean in this page and what was its significance to William Sheppard?

The letters Lapsley sent home during these months ring with an admiration for Sheppard that would have been nearly impossible for a white man to voice for a black home. " The Bateke think there is nobody like ' Mundele Ndom,' the black white man, as they call Sheppard.... His temper is bright and even---- really man of unusual graces and strong points of character. So I am thankful to God for Sheppard." He describes Sheppard as a "born trader... I let him do most of the buying," and speaks admiringly of Sheppard's physical hardiness and his skill at hunting, of his coping with storms that threatened to blow away their tents, and of Sheppard pulling himself fifteen feet down once shot a hippo,jumped into the water to tie a rope around it, and narrowly escaped a crocodile who also had an eye on the hippo.