Use the ‘comment_post”hook in your plugin, an example:

add_action( 'comment_post', 'my_comment_post_callback', 10, 2 );

function my_comment_post_callback( $comment_ID, $comment_approved ) {
// Do something with the comment data
}

To get the author name and metadata about a wordpress comments the ‘get_comment’ hook to get the author name and metadata about a WordPress comment and change it, here is an example:

add_filter( 'wp_get_current_commenter', 'my_commenter_name_callback' );

function my_commenter_name_callback( $commenter ) {
// Change the display name of the author
$commenter['comment_author'] = 'New Display Name';
return $commenter;
}

The following is a list of comment hooks available to WordPress plugins and themes, or additional hooks that will support working with comments.

• comment_form
• add_metabox
• update_comment_meta
• get_comment_meta
• wp_list_comments
• add_comment_meta
• get_comment_meta
• comment_text
• check_comment
• comment_post
• edit_comment
• transition_comment_status
• comment_form_before
• comment_form_top
• comment_from before_fields
• comment_form_after_fields
• comment_form+after

For additional visualization go to: https://wordpress.stackexchange.com/questions/39028/hook-filter-before-and-after-comments

Additional reference for all hooks: The WordPress Hooks Database.