Carson is a bot that currently runs on the symfony/symfony repository. His job is to help automate different issue and pull request workflows.
For an introduction, read: http://symfony.com/blog/calling-for-issue-triagers-a-new-workflow-and-the-carson-butler
Currently, Carson's super powers are used to automatically label issues based on comments from people in the community. This gives anyone the power to review an issue or pull request and comment to update its status. If Carson does his job well (i.e. if it's useful), more features may be added in the future.
For details on how this review / label process works, see http://symfony.com/doc/current/contributing/community/reviews.html