I am a victim of defamation of character per a court document filed.

First, it's not possible to defame someone in a court proceeding, because there's a "litigation privilege" that covers court documents. If there weren't this privilege, almost every lawsuit would spawn another lawsuit. Secondly, a defamation claim requires provably false unprivileged facts told to a 3rd party that damages the target. Statements that are just opinions or allegations aren't facts, so they don't qualify. Some court documents don't even contain statements of fact, such as unverified complaints, which just contain allegations of fact which may or may not be proved. Allegations aren't facts, they're just unproven claims. For very egregious lies under oath, it might be possible to get a DA to criminally prosecute them for perjury. For the garden variety falsities, you can challenge those statements in the court proceeding itself by cross-examining and impeaching the declarant of the statements. Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.

Most statements made in court are privileged, and cannot be used as the basis of a defamation lawsuit. This includes written documents. For more on the litigation privilege, see California Civil Code Section 47.