There are a few possible reasons why you might see "Denis" with one "n" sometimes:
* Typographical Error: It could be a simple mistake.
* Foreign Language Influences: In some languages, the name is spelled with one "n". It might be a transliteration error, especially if it's coming from a non-English source.
* Creative License: Some authors or artists might choose to use alternative spellings for artistic reasons, especially if they are writing in a fictional setting or creating a unique character.
However, in general, it's safe to assume that the correct spelling is always "Dennis" with two "n"s.