How to Add Sender’s Name to Order Comments in Magento2 Admin

You need to override the following file:

vendor/magento/module-sales/Controller/Adminhtml/Order/AddComment.php

After that inject \Magento\Backend\Model\Auth\Session like below:

public function __construct(
    ...
    \Magento\Backend\Model\Auth\Session $authSession
    ...
){
    ...
    $this->authSession = $authSession;
    ...
}

Under execute function add the below line:

$username = $this->authSession->getUser()->getUsername();
$append = " (by ".$username.")";
$history = $order->addStatusHistoryComment($data['comment'].$append, $data['status']);

In place of

$history = $order->addStatusHistoryComment($data['comment'], $data['status']);

All done. After that you can edit anything from admin will show the admin username to the comments.

If you want to edit the core file AddComment.php then you can add the following code to your AddComment.php. But this is not a good practice to modify core files directly. Best way is to override that file and work accordingly. Code for AddComment.php:

<?php
/**
 *
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\Sales\Controller\Adminhtml\Order;

use Magento\Backend\App\Action;
use Magento\Sales\Model\Order\Email\Sender\OrderCommentSender;

use Magento\Sales\Api\OrderManagementInterface;
use Magento\Sales\Api\OrderRepositoryInterface;
use Magento\Framework\Exception\NoSuchEntityException;
use Magento\Framework\Exception\InputException;
use Psr\Log\LoggerInterface;

class AddComment extends \Magento\Sales\Controller\Adminhtml\Order
{
    /**
     * Authorization level of a basic admin session
     *
     * @see _isAllowed()
     */
    const ADMIN_RESOURCE = 'Magento_Sales::comment';

    /**
     * Core registry
     *
     * @var \Magento\Framework\Registry
     */
    protected $_coreRegistry = null;

    /**
     * @var \Magento\Framework\App\Response\Http\FileFactory
     */
    protected $_fileFactory;

    /**
     * @var \Magento\Framework\Translate\InlineInterface
     */
    protected $_translateInline;

    /**
     * @var \Magento\Framework\View\Result\PageFactory
     */
    protected $resultPageFactory;

    /**
     * @var \Magento\Framework\Controller\Result\JsonFactory
     */
    protected $resultJsonFactory;

    /**
     * @var \Magento\Framework\View\Result\LayoutFactory
     */
    protected $resultLayoutFactory;

    /**
     * @var \Magento\Framework\Controller\Result\RawFactory
     */
    protected $resultRawFactory;

    /**
     * @var OrderManagementInterface
     */
    protected $orderManagement;

    /**
     * @var OrderRepositoryInterface
     */
    protected $orderRepository;

    /**
     * @var LoggerInterface
     */
    protected $logger;

    protected $authSession;

    public function __construct(
        Action\Context $context,
        \Magento\Framework\Registry $coreRegistry,
        \Magento\Framework\App\Response\Http\FileFactory $fileFactory,
        \Magento\Framework\Translate\InlineInterface $translateInline,
        \Magento\Framework\View\Result\PageFactory $resultPageFactory,
        \Magento\Framework\Controller\Result\JsonFactory $resultJsonFactory,
        \Magento\Framework\View\Result\LayoutFactory $resultLayoutFactory,
        \Magento\Framework\Controller\Result\RawFactory $resultRawFactory,
        OrderManagementInterface $orderManagement,
        OrderRepositoryInterface $orderRepository,
        LoggerInterface $logger,
        \Magento\Backend\Model\Auth\Session $authSession
    ) {
        $this->authSession = $authSession;
        parent::__construct($context, $coreRegistry,$fileFactory,$translateInline,$resultPageFactory,$resultJsonFactory,$resultLayoutFactory,$resultRawFactory,$orderManagement,$orderRepository,$logger);
    }

    /**
     * Add order comment action
     *
     * @return \Magento\Framework\Controller\ResultInterface
     */
    public function execute()
    {
        $order = $this->_initOrder();
        if ($order) {
            try {
                $data = $this->getRequest()->getPost('history');
                if (empty($data['comment']) && $data['status'] == $order->getDataByKey('status')) {
                    throw new \Magento\Framework\Exception\LocalizedException(__('Please enter a comment.'));
                }

                $notify = isset($data['is_customer_notified']) ? $data['is_customer_notified'] : false;
                $visible = isset($data['is_visible_on_front']) ? $data['is_visible_on_front'] : false;

                $username = $this->authSession->getUser()->getUsername();
                $append = " (by ".$username.")";

                $history = $order->addStatusHistoryComment($data['comment'].$append, $data['status']);
                $history->setIsVisibleOnFront($visible);
                $history->setIsCustomerNotified($notify);
                $history->save();

                $comment = trim(strip_tags($data['comment']));

                $order->save();
                /** @var OrderCommentSender $orderCommentSender */
                $orderCommentSender = $this->_objectManager
                    ->create(\Magento\Sales\Model\Order\Email\Sender\OrderCommentSender::class);

                $orderCommentSender->send($order, $notify, $comment);

                return $this->resultPageFactory->create();
            } catch (\Magento\Framework\Exception\LocalizedException $e) {
                $response = ['error' => true, 'message' => $e->getMessage()];
            } catch (\Exception $e) {
                $response = ['error' => true, 'message' => __('We cannot add order history.')];
            }
            if (is_array($response)) {
                $resultJson = $this->resultJsonFactory->create();
                $resultJson->setData($response);
                return $resultJson;
            }
        }
        return $this->resultRedirectFactory->create()->setPath('sales/*/');
    }
}

After the changes run the below commands:

bin/magento setup:di:compile

bin/magento setup:static-content:deploy -f

(if needed)(-f if developer mode and default mode enabled)

Hope this helps!