Michael (Ascension of the Cybermen)

In the Matrix-constructed story behind which hid the true fate of the Timeless Child, (TV: The Timeless Children) Michael was a thief in Ireland. When the young Garda officer Brendan came after him, Michael pulled out a gun. Despite Brendan trying to reason with him, the terrified Michael shot him, causing Brendan to fall from a cliff and die of his wounds, temporarily. (TV: Ascension of the Cybermen)

In the true story behind these events, the Timeless Child fell from a cliff on Gallifrey, on accident, whilst playing with another child. (TV: The Timeless Children)

Behind the scenes
Michael's name is not mentioned within dialogue, only the end credits. In Chibnall's post-production script, the character was identified simply as "Thief", and "Michael" was instead the name of the local Sergeant (who is not named at all in the broadcast episode).