remove_user_role
Action Hook: Fires immediately after a role as been removed from a user.
Source: wp-includes/class-wp-user.php:592
WP_User::get_data_by()
Method: Returns only the main user fields.
Source: wp-includes/class-wp-user.php:194
WP_User::set_role()
Method: Sets the role of the user.
Source: wp-includes/class-wp-user.php:606