Formal:
* Orthographic purist: This emphasizes the strict adherence to spelling rules.
* Grammar Nazi: While often used in a negative way, it directly refers to someone who focuses on correct grammar and spelling.
Informal:
* Spelling stickler: This highlights their insistence on accurate spelling.
* Word nerd: This term implies a passion for language in general, which may include a strong interest in spelling.
* Spelling bee enthusiast: This suggests a competitive drive to excel at spelling.
Ultimately, the best term depends on the specific context and the way you want to portray this person's obsession.