It's a great question!
It is posed by Theseus, who reacts to Heracles at the close of Euripides' play, in response to seeing the hero utterly undone after discovering that he has succumb to madness and killed his wife and children. This Heracles, in this moment, has just finished the twelve labors, which he is well known for. The Heracles that completed these feats, which include slaying, subduing and capturing all kinds of monsters, is a hero. The Heracles that stands before Theseus, drenched in the blood of his family, is a murderer. He barely has the will to continue living, and he really wants a hug from his stepdad (his mortal father, Amphitryon). In this play and outside it, there are multiple versions of Heracles.
That is one of the central points that critic Jan Kott makes in the chapter of his book, The Eating of the Gods, that treats on Heracles. Jan Kott is probably best known for writing Shakespeare Our Contemporary, which was revolutionary in making a place for Shakespeare on the modern stage. Though Eating of the Gods is perhaps a less monumental work, it nevertheless offers considerable insight into this character that we are trying to get to know with our 2019 project.
Theseus is certainly aware that Heracles stands right in front of him. But the famed hero that everybody was so looking forward to celebrating is seemingly vanished. Instead, we have a man destroyed by fate, a victim of the goddess Hera's wrath. There are other versions of Heracles besides these two, even. There is a comic Heracles, that appears in Aristophanes' comedy, The Frogs, several satyr plays, and even a few of the straight-up tragedies. There is the mortal Heracles that cannot escape his fate, and the will of the gods, and then the immortal Heracles that lives up on Olympus. There's the shade of Heracles that will forever wander the underworld, and then the Heracles that will be forever remembered for his heroic deeds.
Jan Kott touches on all of these, and introduces us to more as we exit antiquity and arrive in medieval times. Heracles pops up in Shakespeare, not as a character himself but as a reference that holds meaning to characters in crisis. Over the years, he has had many faces, and with these two commissions, "he" will find a few more.
And actually, Theseus, I think we found the famous Heracles. He's everywhere at once. He is at once all of these of these aspects. That's a hard thing to be, as a human, torn in so many directions. Maybe it's why Heracles is so memorable to us though. Maybe it's why we keep telling his story.