The Losers soon learn that this mysterious creature takes the shape of their deepest fears, which is why they start referring to this creature as “IT”, but its preferred and most common shape is Pennywise, the Dancing Clown, as clowns are a common fear among kids and adults.
In the novel, It claims that its true name is Robert "Bob" Gray, but decided to be named “It”. Throughout the book, It is generally referred to as male, usually appearing as Pennywise.
Since It's true identity is unclear, due to its shape-shifting abilities and being from another universe, It's real name and species are also called Deadlights, but few know this, which is why it's referred to as IT.
The Pennywise the clown origin story sees an ancient, evil being that is perhaps as old as the universe itself. In the novel, however, the entity IT/Pennywise has a real name — Bob Gray. Bob Gray isn't human, however, and shares the same origin as IT.
In both the book and the films, It is an ancient alien creature, older than civilization, and in King's novel, older than our universe. It feasts on the flesh of humans simply because our fears are easy to manifest and they make us taste better.
As well as having his right arm bitten off, Georgie is trying to crawl away but he was dragged into the sewers and devoured by Pennywise, with an unnamed older woman and her cat being the sole witnesses of the horrific scene, including before Georgie lost his arm.
Weakened, IT runs away to tend its wounds and is chased by Bill, Richie, and Ben, who stays behind to destroy the eggs laid by IT. Bill then fights his way inside IT's body to get to its heart, crushing it and finally killing the creature.
Muschietti appears to be implying Pennywise was a human familiar who It corrupted and then enjoyed so much It incorporated his shape into its file cabinet of monsters.
In the novel, It's origins are nebulous. He took the form of a clown most frequently, Mr. Bob Gray or Pennywise, but his true form is an ancient eldritch entity from another universe who landed in the town that would become Derry by way of an asteroid and first awoke in 1715.
Throughout Stephen King's It, Pennywise is referred to as a male, but author Stephen King pulled a fast one on readers in the It book ending by revealing the creature's true form was a pregnant spider, implying that it is, in fact, biologically female.
Kersh is Pennywise's daughter.
What symbolizes a child's sense of imagination is manipulated to lure children to the clown, Pennywise (Bill Skarsgård). Pennywise's most notable ability is to manifest as each of the children's fears. Whenever the red balloon appears, it signals that Pennywise is close, if not already present.
This is one of the most interesting Hollywood couplings we learned about in quite some time. Apparently, Pennywise and the Babadook are dating. In fact, they're in a long term committed relationship.
Still, the film gives viewers a pretty good sense of who Bill (Jaeden Lieberher), Beverly (Sophia Lillis), Ben (Jeremy Ray Taylor), Richie (Stranger Things star Finn Wolfhard), Eddie (Jack Dylan Grazer ), Stanley (Wyatt Oleff), and Mike (Chosen Jacobs) are.
Throughout the summer and their trials against Pennywise and the school bullies, the Losers realize that none of the adults in Derry can actually see Pennywise or the horrors he is committing against the children of Derry.
Pennwise is (biologically) asexual and has the ability to reproduce. Therefore even though King describes pennywise as a female further into the book, 'IT' is (technically) neither male nor female. IT manifests itself as the the thing you fear most. In the case of one child it turns out to be a clown.
Out of all the characters in Stephen King's works, the scariest is, without a doubt, Pennywise from It. Because Pennywise isn't given a tragic backstory in the films, all viewers know is that the killer clown is a paranormal entity who resides in drains and lures in children.
A god of destruction, not just of our world, but of multiple worlds and even multiple universes. It originated in a vast cosmic void between worlds that has been called, at times, the Macroverse, and in King's Dark Tower series, the Todash Darkness, in a space It refers to only as the Deadlights.
Humiliated, Pennywise begins to shrink, transforming into an almost Benjamin Button–like, melted clown-baby.
It may reproduce via parthenogenesis, like the copperhead snake, or something similar. It never did before because it never HAD to, or even thought to. But after almost being killed by the losers the first time, it realized it may in fact NEED to reproduce to continue its existence.
It disguises itself as many frightening things in the movie. Pennywise can morph his mouth into a giant gaping mouth with layers of sharp teeth which he uses it mangle and eat his victims.
Film: At the house on Neibolt Street, the kids basically do a bunch of damage by impaling It with rods. It looks like they get these weapons from the rusty wrought-iron fence of the house itself. Down in the sewers, during their final encounter, it's much of the same.
Both being interdimensional entities, their powers are at the same level, meaning that the turtle could kill IT if it wanted to. It makes sense that IT is afraid of Maturin – but the viewers and readers also have genuine grounds for cosmic terror.