In the books, Bosch is very secretive of his identity, but we do find out many factoids about him. He loves chocolate (dark) and cheese, hates mayonnaise because he almost drowned in it (true story) and comes very close to not telling the Secret Series story at all. He also had a pea attached to his thigh as a young child. He seems to enjoy making his books as stressful as possible for readers, and has only said "I'm sorry" one documented time (at least sincerely). This is ironic because he seems to not want to write these books at all. Before any book he writes, usually in the introductions, he warns his readers to stop reading before it's too late, but the readers read it anyway. He often tries to give helpful advice on how to make the Secret series books as inconspicuous looking as possible, usually by giving helpful ways to disguise their book. He appears to be living with a snarky rabbit named Quiche and a cat named Cacao.Edit
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The following contains major plot details about the series. Turn back now and pretend like you didn't see anything! Perhaps listen to some nice music.. That's better.
Pseudonymous Bosch, as revealed in You Have to Stop This, is really Max-Ernest. He reveals this in the epilogue, after Max-Ernest's speech, where he says "Well, what did you think of my speech? Pretty good for a kid, right?" This means he is truly Max-Ernest. There were a few hints throughout the series,such as, Max-Ernest's initials are M.E.,which could stand for me. And Pseudonymous Bosch seems to like the same things as Max-Ernest, such as chocolate. Also, it is revealed in the fourth book This Isn't What it Looks Like that Max-Ernest becomes a writer. He also sees himself eating chocolate something PB seems to love. In the same chapter, Max-Ernest peers into a mirror and he sees himself in the future, writing something like "I can't keep a secret. Never could." Since Pseudonymous Bosch used those words in his very first book, it means Max-Ernest in the future will write about their adventures. It is also shown at the end of the book Bad Magic that he is Max-Ernest when he says "Eventually, of course, he would get that chance, but by then he would have many more jokes - and many more adventures - to tell me about." when he speaks about Max-Ernest's brother (a.k.a. his brother) Paul-Clay.