Så vidt jeg ved, er fortælleren også hovedpersonen.

It is a fixed expression meaning as far as I know or to the best of my knowledge.

It shows that the speaker is not claiming absolute certainty. Literally, it is something like so/far as I know, but in natural English you would normally translate it as as far as I know.

In this expression, it is normally written as two words: så vidt.

So the standard form here is:

Så vidt jeg ved

not såvidt jeg ved.

This is because Danish main clauses follow the V2 rule: the finite verb must come in the second position.

The basic statement is:

Fortælleren er også hovedpersonen.
= The narrator is also the main character.

When Så vidt jeg ved is moved to the front, it takes the first position. That forces the verb er into second position:

Så vidt jeg ved, er fortælleren også hovedpersonen.

So this word order is completely normal in Danish.

Because jeg ved is inside the expression så vidt jeg ved, where the clause has normal subordinate-clause order.

In Danish, subordinate clauses usually keep subject + verb order:

jeg ved = I know

So:

så vidt jeg ved
not så vidt ved jeg

Even though ved jeg can appear in some other structures, it would not be the normal form here.

It is:

• fortæller = narrator / storyteller
• -en = the definite singular ending for a common-gender noun

So:

fortælleren = the narrator

This is very common in Danish: instead of a separate word for the, Danish often adds the article to the end of the noun.

Because Danish usually marks definiteness with an ending attached to the noun.

For example:

• en fortæller = a narrator
• fortælleren = the narrator

and

• en hovedperson = a main character
• hovedpersonen = the main character

So the English word the is often expressed by -en, -et, or -ne in Danish, depending on the noun.

It comes from the compound noun hovedperson:

• hoved = head / main
• person = person

So hovedperson means main character or protagonist.

Then -en makes it definite:

hovedpersonen = the main character

Because Danish writes many compound nouns as one word, much more often than English does.

So:

• hovedperson = main character
• fortællerstemme = narrative voice
• barndomshjem = childhood home

For English speakers, this is very important to get used to: if English has a noun + noun combination, Danish will very often write it as one single word.

Også means also or too.

In this sentence, it comes after the verb:

er fortælleren også hovedpersonen

That is a normal position for også in a main clause like this. It tells us that the narrator has an additional role: the narrator is also the main character.

Compare:

• Fortælleren er også hovedpersonen.
• Så vidt jeg ved, er fortælleren også hovedpersonen.

Both are natural.

Sometimes yes, but changing its position can slightly change the emphasis.

The sentence here is the most neutral and natural version:

Så vidt jeg ved, er fortælleren også hovedpersonen.

If you move også, the sentence may still be possible, but the rhythm or focus changes. As a learner, the safest choice is to keep også where it is here.

The comma separates the introductory expression Så vidt jeg ved from the main clause.

So the structure is:

• introductory comment: Så vidt jeg ved
• main statement: er fortælleren også hovedpersonen

This kind of comma is very common in Danish writing.

Yes, absolutely.

That version is also natural and means the same thing overall.

The difference is mostly about emphasis:

• Så vidt jeg ved, er fortælleren også hovedpersonen.
  = starts by signaling uncertainty

• Fortælleren er også hovedpersonen, så vidt jeg ved.
  = gives the statement first, then adds the speaker’s caution at the end

Both are good Danish.

The core statement is:

Fortælleren er også hovedpersonen.

Then the speaker adds the introductory phrase:

Så vidt jeg ved, ...

So it can help to learn it in two steps:

1. Fortælleren er også hovedpersonen.
2. Så vidt jeg ved, er fortælleren også hovedpersonen.

That makes the word order easier to understand.