Programmatically Create a User in WordPress

functions.php

<?php
// Programmatically Create a User in WordPress
add_action('init', 'prefix_add_user');
function prefix_add_user() {
    $username = 'username123';
    $password = 'pasword123';
    $email = 'drew@example.com';

    $user = get_user_by( 'email', $email );
    if( ! $user ) {

        // Create the new user
        $user_id = wp_create_user( $username, $password, $email );
        if( is_wp_error( $user_id ) ) {
            // examine the error message
            echo( "Error: " . $user_id->get_error_message() );
            exit;
        }

        // Get current user object
        $user = get_user_by( 'id', $user_id );
    }

    // Remove role
    $user->remove_role( 'subscriber' );

    // Add role
    $user->add_role( 'administrator' );
}