Ashad

A Cyberman, originally known as Ashad, was given the name of the Lone Cyberman.

Origin
Originally a humanoid, Ashad had multiple children before undergoing cyber-conversion, transforming him into a Cyberman. He did not have an emotional inhibitor, stating he "[did] not need to be stabilised". As he recalled to the Thirteenth Doctor and Mary Shelley, his children joined the resistance and so he slit their throats. (TV: The Haunting of Villa Diodati)

Forewarning
Captain Jack Harkness once tried to contact the Doctor to warn him and "beware of the Lone Cyberman" and to not give it what it wants. However, he got hold of Ryan Sinclair, Yasmin Khan and Graham O'Brien instead, initially believing them to be the new Doctor. When he was told that he was she, he told them to warn her instead and tell her about a fallen empire. (TV: Fugitive of the Judoon)

Searching for the Cyberium
Ashad travelled back in time to 1816 to attempt to extract the Cyberium, the database of Cyberman history, from Percy Shelley. The Thirteenth Doctor absorbed it herself, knowing Shelley's death would alter the future. However when Ashad threatened to tear reality by summoning his ship, she relinquished the Cyberium to him, knowingly ignoring Captain Jack's warning but deciding she would rather confront the Cybermen in the future than change the course of history by having the Earth destroyed in 1816. After taking the Cyberium, Ashad disappeared. (TV: The Haunting of Villa Diodati)