Who's Dr. Phosphorus?

Who's This? A radioactive skeleton.

The facts: Created by Steve Englehart and Walt Simonson in Detective Comics #469 (May 1977), Dr. Phosphorus wanted to build a nuclear reactor in Gotham, but the citizens sent him packing and he was irradiated far from town when his facility melted down. He appeared a few times in Batman comics, but never became an A-lister there. Underworld Unleashed gave him an upgrade and he became something of a concern in James Robinson's Starman series. He managed to survive his eventual death there (see below) and showed up in Batman comics of the 2000s, also appearing in Titans, and in the New52 era, Catwoman, Batgirl, and Forever Evil.
How you could have heard of him: He cuts a distinctive figure, so while he's rarely used as the focus of a story, he does appear in the background a lot in the contemporary era. He will apparently be a member of HBO's Creature Commandos (voiced by Alan Tudyk).
Example story: Detective Comics #825 (January 2007) "The Return of Dr. Phosphorus!" by Royal McGraw, Marcos Marz, Luciano del Negro and John Kalisz
Dr. Phosphorus is always "returning" (there seem to be a number of stories that say so in the title), but like the black and white cover here, he just seems to inspire a kind of Universal Monster movie atmosphere. Like a lot of Batman villains, you might say - Man-Bat, the original Clayface and so on - but perhaps others appear too often to turn ALL their stories into a kind of retro-horror tale. Phosphorus appears just infrequently enough to allow for a dip into that style. Not that any of the stories are THAT stylized. Still, Cadmus IS full of mad scientists, and that's where they've been keeping our boy Alex Sartorius.
That rather poetic guy even has a connection to Phosphorus' origins.
Dude stole his life savings and made him turn to crime. Now he's going to steal the secrets of his physiology to make billions off the patents for... radioactive immortality? Who knows? Nice of Cadmus not to keep propriety rights from its employees though. Less nice that they apparently power this facility by siphoning energy from Doctor Phosphorus! And so when the power cuts out, the scientists know they're in trouble.
Man, he is hard to read. And I don't mean the lack of facial features. Later, Commissioner Gordon calls Batman to the burnt-out site. Glowing footprints provide a clue, as does the ball of glowing ash that almost takes Gordon's hand off. And its odour. Like garlic. Phosphorus pentoxide. Well, at least we know the Doc is safe from vampires. But not from Batman!

One of Phosphorus' originators is dead (his pal just horribly burned). He next goes after another scientist who was involved, but Batman is waiting for him.
But Phosphorus is too angry to sit still and he manages to slash at Batman anyway. As the Bat falls off the building scarred, presumably forever (Bruce Wayne has a plastic surgeon on retainer), the scientist dude is sent to hell.
But sadistically, this actually doesn't kill him. Rather, one of those explosive ash balls does.
Crime boss Rupert Thorne is the third man on revenge list (and he's had a smouldering hard-on for these guys for 30 years, by our count). Thorne is a name we recognize, so while the world might actually be better without him in it, it's a safe bet that Batman will prevent Phosphorus from killing him. Alfred's acid reflux gives Batman an idea: Baking soda. Let's burp that garlic right out! Thorne is at Blackgate Prison being protected by the Commish himself. Another hero whose burns should have been permanent, but will magically disappear by the next story.
Before Sartorius can boil Thorne alive, however, the Bat shows up armed with home-made fire retardant.
There's also an Arm & Hammer joke to be made here, but the Bat don't shill. Phosphorus is sent to the less corrupt S.TA.R. Labs for containment and Bruce Wayne has a spit take when Alfred offers him some terrible beignets made without the benefit of baking soda. They were fresh out!

So does Dr. Phosphorus deserve a place in Batman's Rogues' Gallery? Sure. The horror elements work well, etc. But perhaps Firebug is a more versatile fire-related villain for the Bat. All in all, it probably made sense that Sartorius had his best years in Starman's Opal City.

Who's Next? A magnetic madman.