After finding the Dwarf Planet Eris, which is overrun with the disgusting and parasitic Infested, you find the blueprints to a warframe that can somewhat control the infestation, and after finding the rest of his blueprints you build him in your foundry and equip him shortly after. He looks around confused but quickly adapts

I take it you are my new mast- Ahem, operator. Well If so, then I am Nidus.