Taken from “Is Phineas and Candace’s Real Dad Doofenshmirtz?” from Juliusroot5′s Phineas and Ferb Wiki user page, slightly modified.
The Big Question
Now, I’ve noticed that there have been some major rumors going around that Doofenshmirtz-that’s right, the Doc himself- is Candace and Phineas’ real father. This is a big question, and I have seen some theories that really impressed me. Personally, I absolutely, 100% believe that Doofenshmirtz is Candace and Phineas’ real father and I have posted my theory below.
If (and when) Doofenshmirtz was cheating on Charlene with Linda, he would’ve made sure to have Vanessa first (because I figure she’s about 17) to keep Charlene from becoming suspicious, then he would’ve got together with Linda and had Candace. Doofenshmirtz seems smart enough(i mean look at his inventions!), so he would’ve known not to introduce Linda and Charlene or else have major complications.
He would’ve then had Phineas with Linda shortly before the divorce. Linda would’ve probably seen some of Doofenshmirtz evil schemes and thought him crazy, so she ditched him once Phineas was born. Also, it seems that Charlene may have been the one who filed for divorce, not Doofenshmirtz, because Charlene does occasionally show dislike to Heinz, while he never really indicates any dislike towards her.
True, he once ripped up a picture of her, but I believe that was more out of anger for her divorcing him. It also seems that, after the divorce, Heinz had full-custody of Vanessa for a while. The main thing that indicates this is when Heinz pulls out his wallet to show Perry his pictures of Vanessa and, whereas both Heinz and Vanessa are present in all of the pictures (and it looked like a lot of pictures), Charlene was not clearly visible in any of them. So he would’ve forgotten about Linda, Candace, and Phineas because he now had to raise a child on his own. I believe that Charlene just wanted to spend more time with Vanessa, so she took Heinz to court and they had the custody changed to alternating weeks(in other words, Vanessa would spend a week with her father then a week with her mother, etc.)
Also, Candace has a long neck, and there are actually several indications of Doofenshmirtz having a long neck. For example, his knees are often bent and he has a self-proclaimed “mantis-like posture”, which can be described as a constant slouch. Plus, his neck is always at an angle by which a camera would capture it as a short-view. This all indicates that his neck is actually longer(possibly much longer) than his design lets on.
Another thing is that Doofenshmirtz was short when he was a child, and both Phineas and Candace are short for their age (Indicated in Phineas’s design and in “Attack of The 50 foot Sister”, an episode in which Candace is too short to be the new “Flawless Girl”.) Also, when Linda married Lawrence, there was no current father figure in Candace’s life and so the only father she has known is Lawrence (notice how she calls him “Dad” instead of “Lawrence”. Most kids would call their stepfather by his real name, but Candace does not because she feels a more father-daughter-like relationship because he is the only father she has known).
Also, some people have been saying that in the episode “What Do It Do?” Doofenshmirtz states that once Linda breaks up with him he never sees her again, and I must admit that I also heard him say that, but think about this: maybe he was so embarrassed about the fact that he had cheated on his wife with a past love that he didn’t want to mention it. Also, he meets Candace several times in the show, but they neither recognize each other. This would make sense because once Linda had Candace, Doofenshmirtz had Vanessa at home to worry about, thus meaning that he rarely saw Candace, and Linda was probably so ashamed that she had had a kid without getting married that she never told Candace that this strange man was her father.
I believe that Linda and Doofenshmirtz got together again shortly before the divorce and Linda got pregnant from him without actually meaning to and, not wanting to have an abortion, gave birth to Phineas. I believe that Phineas was born just after Charlene divorced Doofenshmirtz and that Heinz would’ve been so busy with raising Vanessa by himself that he never returned to Linda. So, after awhile he forgot about Candace and Phineas and could only remember Linda becuase she was the one he had fallen in love with.
Also, if Heinz and Phineas do ever meet, Phineas would not recognize Heinz because he would already have been divorced and been caring for Vanessa by the time Phineas was born. And if Candace had seen him and he had seen Candace, that would’ve been in about 1995 (Candace is 15 and I like to think that Heinz is 45) which would mean that they both would have aged some and probably look a lot different, or at least different enough to not recognize each other.
Similarities between Phineas, Candace and Heinz
Phineas and Doofenshmirtz both have the same ears, eyes, hair, and they both have the basic triangle head shape, and I also noticed that they smile the same when laughing or making an open-mouth smile.Plus, Heinz is very intelligent and a great inventor(not to mention a fast inventor), and it’s quite easy to see that the same can be said about Phineas.
Another trait they have in common is kindness. Even though Doofenshmirtz is “Evil”, the kindness and gentleness inside him comes out when he is with Vanessa, and it’s pretty obvious to see that he loves her very very much. One more thing is that Doofenshmirtz has that little crick in his neck that makes it slant, and this crick is developing in Phineas, though it looks like it will be less pronounced than Doofenshmirtz’s.
So, I guess that my point is that Heinz is Candace and Phineas’s father and that he simply fell in love with 2 women at the same time.