Xylo Jones

Xylo Jones was a human corpse, upgraded into a Cyberman after his death and kept in a cell of dark water by 3W.

The Twelfth Doctor and Clara viewed Jones' skeleton shortly after their arrival, not knowing that he was a Cyberman. Upon Missy's command, Jones left his cell and marched out of the doors of St. Paul's Cathedral with the rest of the converted bodies. (TV: Dark Water)