In the standardized Old Norse orthography, the name is spelled Níðhǫggr, but the letter 'ǫ' is frequently replaced with the Modern Icelandic ö for reasons of familiarity or technical expediency.
The name can be represented in English texts with i for í; th, d or (rarely) dh for ð; o for ǫ and optionally without r as in Modern Scandinavian reflexes.