diff --git a/core/modules/comment/comment.admin.inc b/core/modules/comment/comment.admin.inc
index 51158a9..faafc86 100644
--- a/core/modules/comment/comment.admin.inc
+++ b/core/modules/comment/comment.admin.inc
@@ -113,6 +113,10 @@ function comment_admin_overview($form, &$form_state, $arg) {
     // Remove the first node title from the node_titles array and attach to
     // the comment.
     $node_title = $comment->nid->entity->label();
+    $username = array(
+      '#theme' => 'username',
+      '#account' => comment_prepare_author($comment),
+    );
     $options[$comment->id()] = array(
       'subject' => array(
         'data' => array(
@@ -122,7 +126,7 @@ function comment_admin_overview($form, &$form_state, $arg) {
           '#options' => array('attributes' => array('title' => truncate_utf8($comment->comment_body->value, 128)), 'fragment' => 'comment-' . $comment->id()),
         ),
       ),
-      'author' => theme('username', array('account' => comment_prepare_author($comment))),
+      'author' => drupal_render($username),
       'posted_in' => array(
         'data' => array(
           '#type' => 'link',
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index 9895b1f..5c8bacb 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -554,7 +554,11 @@ function theme_comment_block($variables) {
   }
 
   if ($items) {
-    return theme('item_list', array('items' => $items));
+    $item_list = array(
+      '#theme' => 'item_list',
+      '#items' => $items,
+    );
+    return drupal_render($item_list);
   }
   else {
     return t('No comments available.');
@@ -615,8 +619,12 @@ function comment_node_view(EntityInterface $node, EntityDisplay $display, $view_
           }
         }
         else {
+          $comment_post_forbidden = array(
+            '#theme' => 'comment_post_forbidden',
+            '#node' => $node,
+          );
           $links['comment-forbidden'] = array(
-            'title' => theme('comment_post_forbidden', array('node' => $node)),
+            'title' => drupal_render($comment_post_forbidden),
             'html' => TRUE,
           );
         }
@@ -645,8 +653,12 @@ function comment_node_view(EntityInterface $node, EntityDisplay $display, $view_
           }
         }
         else {
+          $comment_post_forbidden = array(
+            '#theme' => 'comment_post_forbidden',
+            '#node' => $node,
+          );
           $links['comment-forbidden'] = array(
-            'title' => theme('comment_post_forbidden', array('node' => $node)),
+            'title' => drupal_render($comment_post_forbidden),
             'html' => TRUE,
           );
         }
@@ -948,7 +960,11 @@ function comment_links(Comment $comment, EntityInterface $node) {
       );
     }
     if (empty($links)) {
-      $links['comment-forbidden']['title'] = theme('comment_post_forbidden', array('node' => $node));
+      $comment_post_forbidden = array(
+        '#theme' => 'comment_post_forbidden',
+        '#node' => $node,
+      );
+      $links['comment-forbidden']['title'] = drupal_render($comment_post_forbidden);
       $links['comment-forbidden']['html'] = TRUE;
     }
   }
@@ -1573,7 +1589,11 @@ function template_preprocess_comment(&$variables) {
 
   $account = comment_prepare_author($comment);
   // @todo Do not call theme() here. We do this for purposes of t().
-  $variables['author'] = theme('username', array('account' => $account));
+  $username = array(
+    '#theme' => 'username',
+    '#account' => $account,
+  );
+  $variables['author'] = drupal_render($username);
   $variables['new'] = $comment->new->value ? t('new') : '';
   $variables['created'] = format_date($comment->created->value);
   // Avoid calling format_date() twice on the same timestamp.
@@ -1613,7 +1633,11 @@ function template_preprocess_comment(&$variables) {
     $account_parent = comment_prepare_author($comment_parent);
     $variables['parent_comment'] = $comment_parent;
     // @todo Do not call theme() here. We do this for purposes of t().
-    $variables['parent_author'] = theme('username', array('account' => $account_parent));
+    $username = array(
+      '#theme' => 'username',
+      '#account' => $account_parent,
+    );
+    $variables['parent_author'] = drupal_render($username);
     $variables['parent_created'] = format_date($comment_parent->created->value);
     // Avoid calling format_date() twice on the same timestamp.
     if ($comment_parent->changed->value == $comment_parent->created->value) {
diff --git a/core/modules/comment/lib/Drupal/comment/CommentFormController.php b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
index dd4e13d..3b9fdcf 100644
--- a/core/modules/comment/lib/Drupal/comment/CommentFormController.php
+++ b/core/modules/comment/lib/Drupal/comment/CommentFormController.php
@@ -92,7 +92,11 @@ public function form(array $form, array &$form_state) {
     elseif ($user->uid) {
       $form['author']['name']['#type'] = 'item';
       $form['author']['name']['#value'] = $form['author']['name']['#default_value'];
-      $form['author']['name']['#markup'] = theme('username', array('account' => $user));
+      $username = array(
+        '#theme' => 'username',
+        '#account' => $user,
+      );
+      $form['author']['name']['#markup'] = drupal_render($username);
     }
 
     // Add author e-mail and homepage fields depending on the current user.
diff --git a/core/modules/comment/lib/Drupal/comment/Plugin/views/field/NcsLastCommentName.php b/core/modules/comment/lib/Drupal/comment/Plugin/views/field/NcsLastCommentName.php
index db5bba9..cf0b09c 100644
--- a/core/modules/comment/lib/Drupal/comment/Plugin/views/field/NcsLastCommentName.php
+++ b/core/modules/comment/lib/Drupal/comment/Plugin/views/field/NcsLastCommentName.php
@@ -62,9 +62,11 @@ function render($values) {
       $account = entity_create('user', array());
       $account->name = $this->get_value($values);
       $account->uid = $values->{$this->uid};
-      return theme('username', array(
-        'account' => $account
-      ));
+      $username = array(
+        '#theme' => 'username',
+        '#account' => $account,
+      );
+      return drupal_render($username);
     }
     else {
       return $this->sanitizeValue($this->get_value($values));
diff --git a/core/modules/comment/lib/Drupal/comment/Plugin/views/field/Username.php b/core/modules/comment/lib/Drupal/comment/Plugin/views/field/Username.php
index 05ceb8f..c32ec3a 100644
--- a/core/modules/comment/lib/Drupal/comment/Plugin/views/field/Username.php
+++ b/core/modules/comment/lib/Drupal/comment/Plugin/views/field/Username.php
@@ -54,10 +54,11 @@ function render_link($data, $values) {
       $account->uid = $this->get_value($values, 'uid');
       $account->name = $this->get_value($values);
       $account->homepage = $this->get_value($values, 'homepage');
-
-      return theme('username', array(
-        'account' => $account
-      ));
+      $username = array(
+        '#theme' => 'username',
+        '#account' => $account,
+      );
+      return drupal_render($username);
     }
     else {
       return $data;
diff --git a/core/modules/comment/lib/Drupal/comment/Plugin/views/row/Rss.php b/core/modules/comment/lib/Drupal/comment/Plugin/views/row/Rss.php
index 2e18fa9..10ed48c 100644
--- a/core/modules/comment/lib/Drupal/comment/Plugin/views/row/Rss.php
+++ b/core/modules/comment/lib/Drupal/comment/Plugin/views/row/Rss.php
@@ -154,11 +154,13 @@ function render($row) {
     $item->elements = $comment->rss_elements;
     $item->cid = $comment->id();
 
-    return theme($this->themeFunctions(), array(
-      'view' => $this->view,
-      'options' => $this->options,
-      'row' => $item
-    ));
+    $build = array(
+      '#theme' => $this->themeFunctions(),
+      '#view' => $this->view,
+      '#options' => $this->options,
+      '#row' => $item,
+    );
+    return drupal_render($build);
   }
 
 }