Who's Big Sir?

Who's This? A man mountain.

The facts: Big Sir first appeared in The Flash #338 (October 1984), introduced around the start of the interminable Trial storyline by Cary Bates and Carmine Infantino. Not the best of creations, given that he was mentally challenged and given the name Dufus P. Ratchett. When Who's Who #2 came out, he'd been in just that introductory story, and it seemed to have resolved itself (see below for details). It was all undone when Keith Giffen decided to include him in the Bwa-ha-ha Injustice League, back to being a dim-witted villain, but otherwise, he would have been completely forgotten. The Injustice League die in 2001's Suicide Squad #1, Big Sir among them.
How you could have heard of him: He has appeared in a few issues of Rebirth-era Flash comics (as an inmate in Iron Heights), and appeared in live action on Season 4 of The Flash TV show (thankfully as DAVID Ratchett, and not mentally impaired, or superhuman for that matter).
Example story: The Flash #339-340 (November-December 1984) by Cary Bates, Carmine Infantino and Frank McLaughlin

Basically, this big bruiser with the mind of a child was kidnapped from an institution by members of Flash's Rogues Gallery, dressed up in a supersuit they bought from the Monitor (ramping up to Crisis, he was appearing everywhere and acting out of character), his memory scrambled by the antenna on his costume, and manipulated into thinking the Flash had hurt beat up the Rogues/his friends.

After they wake up, they call him "B.S." for short, a tell that he might be able to catch if he were smarter. In fact, their cover story didn't have to be this complicated. He doesn't know what amnesia is, and though they say he has the mental acuity of an 8-year-old, 8-year-olds have much better grammar - "If Flash beat up me... and yous... where is he now?" To really get him riled up, they seem to have killed a mouse, Big Sir's favorite animal!

And like that, Big Sir is off to fight the Flash wherever he may be, to get justice for his "little friend". The fight involves a lot of mace-whirling--no, strike that, the damn thing shoots energy versions of itself at the Flash. What a weird weapon.

Meanwhile, Lyra (the future Harbinger) is telling the Monitor all about this, and he admonishes her because once he's sold his stuff to a client, as he's told her before, he doesn't CARE what happens. Well, why should WE, then?! In case you do, keep reading... it's end of issue 339 so the Flash is knocked out and Big Sir flies off with him, to the Rogues' general glee (start crime spree NOW).

Another power that's never been clear in further appearances is that Big Sir can create solid energy chains out of thin air, and he ties Flash up in a cave in what looks like the Badlands. Barry tries to explain to him that he's been tricked by the Rogues, but Dufus gets easily distracted. A furry friend, stranded on a ledge!

And...

It appears Big Sir isn't the most agile tool in the shed either. Flash escapes, saves Dufus AND the unspecifiable animal (InfantiNOOOOOOOOOOOO!!!) and that makes them all friends.

In a few issues' time, Big Sir's intelligence will be enhanced by Gorilla City and he'll have even fewer reasons to play the part of an antagonist. But like I said, Giffen saw the comedic potential in the character and undid it all to include him in his Injustice League. Oh well.

Who's Next? The reverse Superman.