Cyberbrig

According to some accounts, the cyber-converted but still independent Brigadier Lethbridge-Stewart remained active as "the Cyberbrig", a superheroesque figure, (NOTVALID: My Dad's A Cyberman!, The Universal Song Contest & Symphonic Spectacular!) following 's 3W Institute bringing back "every man, woman and child" who'd ever died as a Cyberman, the Doctor's old friend the Brigadier among them. (TV: Death in Heaven)

Creation
In 2014, (COMIC: The Fractures) Lethbridge-Stewart was among the dead of the Earth who were converted into Cybermen by pollen rain clouds in a plot spearheaded by the Master in a new female incarnation who referred to herself as. Using the Cyberman ability to fly, he rescued his daughter who had been blown out of the UNIT presidential plane, showing he had chosen to keep his emotions while uploaded to the Nethersphere. After Danny Pink, a fellow converted soldier, rallied the Cybermen to self-destruct and destroy their clouds, the Brigadier was the last to remain.

He took Kate to a graveyard where he saved the Twelfth Doctor the obligation of destroying their old enemy, by using his wrist blaster to shoot the Master. Recognising his old friend, the Doctor fulfilled a lifelong wish of the Brigadier by saluting him, noting that the Brigadier would never be anywhere else but by his side when Earth and the Doctor faced their darkest day. The Brigadier then flew away to parts unknown, having had his lifelong wish fulfilled but also having the chance to see the Doctor once again. (TV: Death in Heaven)

Return to UNIT
To no one's greater surprise than Kate Stewart's own, the newly-minted "Cyberbrig" continued to shadow his daughter, following her to UNIT HQ where he immediately fell back into old habits; Kate became exasperated with his tendency to sit once more in the Brigadier-General's chair and generally act as though he were still running things. The Cyberbrig intended merely to "sort out a few things for [her]", but his ideas about how to run UNIT were deemed rather antiquated by Kate and the rest of the modern UNIT team; for one thing, the Cyberbrig objected to there being so many women (and so many scientists) around the place, putting UNIT leader Kate in rather a tough spot.

By the time of one of his umpteenth arguments with Kate, the Cyberbrig had taken to wearing a false moustache over the metal plating of his Cyber-helmet to try and look more like his old self; in fact, even when eh'd been the human Lethbridge-Stewart, his moustache had always been false, a fact which he hoped was not known to many. (NOTVALID: My Dad's A Cyberman!)

A brand new gig
Eventually, the Cyberbrig took to using his Cyber-converted body's increased physical ability (such as flying) to act as a sort of superhero. During his adventures as the benevolent vigilante the Cyberbrig, he made use of a false mustache which he could tear off, throw like a boomerang, and then have expand into a sort of tarp with which to catch villains and criminals. On one "chilly" night, the Cyberbrig made use of this ability to defeat the Black Guardian. (NOTVALID: The Universal Song Contest & Symphonic Spectacular!)

Behind the scenes
The comedic potential of Alistair Gordon Lethbridge-Stewart remaining active on 21st century Earth as a Cyberman beyond his gentle cameo in Death in Heaven was first explored in an unlicensed context in a sketch created for the Idiot's Lantern show at Gallifrey One in 2015, simply entitled "CYBER-BRIG". DWM 484 saw Steven Moffat, originator of the concept of the cyber-converted Brigadier in the first place, try his hand at the same joke with the comedic short story My Dad's A Cyberman!, which officialised the moniker of "Cyberbrig" for the metal-plated Brigadier.

A month later, snippets from the Idiot's Lantern skit were featured in an episode of The Fan Show, The Universal Song Contest & Symphonic Spectacular!, thus officialising some (though not all) of what Bob Mitsch, Scott Sebring and Athena Stamos had added to the parodical "Cyberbrig mythos".