diff --git src/wp-includes/class-wp-user.php src/wp-includes/class-wp-user.php
index 73f7cdf0d5..4f9fda585d 100644
--- src/wp-includes/class-wp-user.php
+++ src/wp-includes/class-wp-user.php
@@ -166,7 +166,17 @@ class WP_User {
 	 * @param int    $site_id Optional. The site ID to initialize for.
 	 */
 	public function init( $data, $site_id = '' ) {
-		$this->data = $data;
+		/**
+		 * Filters the user data.
+		 * 
+		 * @since 5.3
+		 * 
+		 * @link https://core.trac.wordpress.org/ticket/44094
+		 * 
+		 * @param  object  $data    User DB row object.
+		 * @param  integer $site_id Optional. The site ID.
+		 */
+		$this->data = apply_filters( 'init_user_data', $data, $site_id );
 		$this->ID   = (int) $data->ID;
 
 		$this->for_site( $site_id );
diff --git tests/phpunit/tests/user.php tests/phpunit/tests/user.php
index 13824009b6..fa68752539 100644
--- tests/phpunit/tests/user.php
+++ tests/phpunit/tests/user.php
@@ -1631,4 +1631,39 @@ class Tests_User extends WP_UnitTestCase {
 		// Number of exported user properties.
 		$this->assertSame( 11, count( $actual['data'][0]['data'] ) );
 	}
+
+	/**
+	 * Test for the `init_user_data` filter.
+	 *
+	 * @ticket 44094
+	 */
+	function test_init_user_data_filter() {
+		$user_id = self::factory()->user->create(
+			array(
+				'role'       => 'subscriber',
+				'user_login' => 'test_user_login',
+				'user_email' => 'test-email@test.dev',
+				'user_nicename' => 'test_user_nicename'
+			)
+		);
+
+		add_filter( 'init_user_data', function( $data, $site_id ) use ( $user_id ) {
+			// Alter the `$data` of the created user above.
+			if ( $user_id == $data->ID ) {
+				$data->user_login = 'altered_user_login';
+				$data->user_email = 'altered-email@test.com';
+				$data->user_nicename = 'altered_user_nicename';
+			}
+
+			return $data;
+
+		}, 10, 2 );
+
+		$user = get_user_by( 'ID', $user_id );
+
+		$this->assertSame( $user->user_login, 'altered_user_login' );
+		$this->assertSame( $user->user_email, 'altered-email@test.com' );
+		$this->assertSame( $user->user_nicename, 'altered_user_nicename' );
+	}
+
 }