Just like in any given group of people, diversity in personalities has positive impacts on the overall group performance. But what kind of roles or archetypes exist from a review perspective?
A hacker tries to disassemble and tinker with any given aspect of a product in order to understand every single bit of it. Applying a good amount of creativity by thinking out of the box might reveal rare edge cases and other often overlooked or even novel bugs or lack of design.
The historian has a very good understanding of how hardware developed over time. By considering the time at which the software was written the historian can easily apply such knowledge of changed conditions to see if the code was written to cover all these situations. We all know that 640 KB of RAM is enough, right? Classes of bugs which were supposed to be fixed decades ago are still well known to the historian, so if they appear again, they will be directly spotted.
When it comes to standards and specifications, then the librarian knows them all. Mastering such profession means that at any moment a group member has a question, the librarian can quote the relevant documents. Proper categorization also means that common ideas within software are easily spotted and compared. The librarian does not need creativity to find bugs but can rely on work other developers spent in their own projects, which the librarian simply looks up for comparison.
Large groups benefit from moderators to make sure that social aspects within the group itself are properly covered. If a reviewer gets lost or another is too fast, the moderator can remind everyone that this is a group activity and nobody should feel or actually be excluded.
The translator is able to detect the abstract concept of a code and to articulate it in a way that fellow members can grasp the concept even if they do not understand the programming language.
Such an abstraction can help others to apply their skills on the concept without language barriers in their way.
Users of software which is reviewed have a good understanding of the way the software is actually used. Maybe the code is hard to understand but the user can easily help out when it comes to hitting this special feature under review with a real world example. If anyone can judge about the quality of a comment or the documentation, the user is the best one to ask.
Nobody is fully described by just one of these roles and a group can be verify effective even without covering all of them. The most important aspect is: Be excellent to each other! If someone approaches a problem in a different way than you do then it does not imply that it's the wrong way. And if an approach takes longer than the other, be patient. You never know which question arises from different approaches. This also means that seniors should always involve juniors. Never assume that juniors are just there to learn! Good questions of juniors can easily get seniors into trouble coming up with equally good answers.
Having the author of a software product under review in your group can have advantages and disadvantages.
The advantage is that the author can supply the group with information which is not written anywhere, like future direction, historical background or design choices.
The disadvantage is that authors tend to become blind to bugs and design flaws. They know exactly what they wanted to achieve, which is not necessarily what they actually wrote down. By influencing the group with too much information the group may overlook difficult or complex code which they would have had to carefully look through otherwise.
A performing group benefits the most from an author. A learning group should inspect the code first and ask the author afterwards. This is comparable with a book review or public reading. If you ever have the chance to discuss various interpretations of a text with the author, it is best to be prepared by reading it beforehand on your own.