What can someone do if they find out that another co-worker was responsible for getting them fired? This person was an asset to the company, and the other co-worker was purposely submitting bad reviews and talking negatively to management to get the person fired, however these were factual, if blown out of proportion. Every little thing was targeted.
Without a jurisdiction, I'll just say that unless the comments made in the reviews and discussions were false, the individual is unlikely to have any claim, particularly given that you've stated that this occurred over the course of a year.
However, the individual may be able to argue that they were not given sufficient notice of their performance, for example through performance evaluations, and given the length of time, it likely that one would have occurred.
A company may be able to terminate an employee in spite of their overall contributions if they have breached policy - for instance, an otherwise outstanding employee who attracts negative customer reviews based in fact, and who is given ample opportunity and guidance to improve, may cause brand and reputational damage to the company; in this case, it is a commercial decision to retain or terminate the employee.
As for what recourse the employee has, if the comments were factual, then it is likely that they will not have any, unless the employer has not adhered to procedural requirements - for instance, in Australia, you are required to provide an employee the opportunity to have a support person present at any meeting which may result in the employee's termination - or the employer broke some other law - for instance, discrimination, bullying or harassment law.
Unfortunately, the contributions an employee makes does not necessarily negate the harm they do, and complaints based on an employee's performance are completely valid if factual.