I will give evidence that Vecna is the father of El:
1. In the 4 season, they say every now and then with various visual techniques that Henry and El are two sides of the same coin. And sometimes directly. Henry told El that she reminded him of himself. This is also indicated by the frame in which they look at their tattoos and at a cursory glance 001 and 011 look the same. And Robin once said that "he's a number like Eleven only a sick, evil, male, child-murdering version of her..." And this is only a small part of all these hints. To be honest, I don't understand why this is confusing me alone.
It's just that usually in a work of fiction the antagonist is made to look like the protagonist in order to create an allegory that the latter is struggling with himself. With the worst version he can become.
To make the characters look similar, there are usually three methods:
1) They are given similar backstories, in which only one variable differs, because of which they went down different paths.
For example, it was in How to Train your Dragon 3. (to be fair, it was frankly too short there). The main antagonist, Grimmel, is the embodiment of what Hiccup, the main character, could have become if he had killed Toothless in the How to train your dragon 1. Then Hiccup saw himself in the dragon and showed compassion, refusing the popular recognition that he was so eager for. And Grimmel turned out to be more bloodthirsty, and therefore killed the Night Fury, becoming a "hero" in his village. One variable, and lo and behold, the characters are both exact copies and exact opposites, no matter how strange it may sound.
2) Make sure that the essence of the characters was the same, but the antagonist was just angrier. For example, in Spider-Man 3. Eddie Brock there is pleasant. But not like the canonical Brock from the comics, but like... Bizarro-Peter. He's like if Peter was wormy and had no ethics.
3) Both characters adhere to the same conflict. It's just that one has limitations and the other doesn't. Like in the Rise of the Guardians.
As you can see, none of the above is here. The essence of the characters is completely different. Al is a child who was cut off from the outside world all his childhood and was deprived of love and care. She is quite a tragic character. And Henry is not positioned as a tragic character. He is a bloodthirsty misanthrope, sociopath and nihilist with a God complex. And he has been like this since childhood and he has no tragic backstory. And Al is not opposed to him as someone who adheres to a similar or opposite conflict.
So why are there so many hints that they are similar?
The only explanation I personally see is that El is just too much like her father... seriously, they even have facial expressions and habits in many ways similar. Am I not the only one who noticed this?
2. Henry associated her with himself. He has repeatedly said that they are similar. And he said that he was sincerely glad that El was born. Why such affection? Was the fact that Al was an outcast among the other kids in the lab enough for him to consider her like him? If it suddenly turns out that El is his biological daughter, then it will be justified, because in that case she is his creation. Hence the attachment.
I'm waiting, that in 5 season will be like in Harry Potter and the Order of the Phoenix. The protagonist of the whole movie will be afraid that he is becoming like his enemy (and in this case it will be justified, given that the blood of a psychopath flows in El's veins). A couple of times there will be attacks of cruelty and aggression, after which she will reflect, and then in the end she will come to the conclusion that Harry came to (It isn't how your are alike, it's how your not).
What do you think?