Marion and Otto Keller were among the first missionaries of the Pentecostal Assemblies of Canada. Marion pioneered work in Tanganyika. They started mission work at Nyang'ori, near Kisumu, Kenya and established the Pentecostal Assemblies of God in East Africa.

Marion was born in 1889 in Parry Sound, Ontario, Canada. While working as an Anglican school teacher in Parry Sound she felt called to missionary work. She went to a Bible School in New York State where she met Karl Wittich, her first husband. In 1913, together with a young man named Grothaus, they set out for Tanganyika, a German colony.