completionist

This term is most frequently encountered in gaming culture, where it describes a player who pursues 100% completion, including optional side quests and hidden achievements. While it originated in this niche, it has expanded to describe any obsessive drive toward total collection or exhaustive completion in hobbies like stamp collecting or reading a full series of books.

As an adjective, it describes a mindset of meticulousness and thoroughness. It carries a connotation of persistence that can range from disciplined and admirable to compulsive and obsessive, depending on whether the pursuit is seen as a rewarding challenge or a tedious chore.