xxxxxxxxxx
$user_obj = get_user_by('id', 1);
xxxxxxxxxx
$user_info = get_userdata($userID);
echo $user_info->last_name . ", " . $user_info->first_name. ", " . $user_info->user_email;
xxxxxxxxxx
$username = 'your user name';
$user = get_user_by('login', $username);