The only character in The Invisible Man who benefits from his relationship with Griffin is Marvel. He is the only one who undergoes a transformation by the end of the novel. Why Wells decided to make Marvel the only truly rounded character seems to be surprising enough. However, it seems that Wells probably decided to add the Epilogue almost as an afterthought. There is a strong possibility that Wells wanted to add the Epilogue to tie up loose ends, like perhaps what happened to the three diaries? Were the diaries secure? What if they fell into the wrong hands? What happened to the money Griffin had robbed? What about Marvel? He dropped out rather suddenly after the sixteenth chapter!
The transformation that takes place in Marvel at the end is puzzling enough, but then I guess this had to happen because Wells had to make Marvel a credible enough character with whom the diaries could be entrusted. The author portrays Marvel in the Epilogue as someone who has suddenly matured into a 'great thinker', someone who has 'movements [that] are slow' meaning that he is someone who is not likely to make rash decisions. The most radical transformation is perhaps described in the words, 'But he has a reputation for wisdom'. While these changes are related to his attitudes, beliefs, and character, we also see Marvel as someone who has prospered greatly from his association with Griffin. He now runs an inn named The Invisible Man, and on the signboard are images of boots and a hat. The name of Inn is a tribute to Griffin, who ironically was his benefactor, while the pictures on the signboard indicate that he remembers his humble roots! Prosperity has not blinded him from remembering his past! Do his humbleness and maturity make Marvel the best guardian of Griffin's diaries?
The answer to the question of whether Marvel is the best guardian of Griffin's diaries and his secret to invisibility needs to be analysed with reference to the transformation that has taken place in his character. Marvel's prosperity has apparently not blinded him, to the harms that the misuse of the secrets of the diaries might lead to, his own words, "I wouldn't do what he did" suggest that Marvel would never use the secrets of the diaries in a way that would harm the society in any way! It is clear that the harmful secrets of the diaries are safe in the hands of this unlikeliest of characters in the novel!
This brings us to the question of whether he is a safer guardian of Griffin's secrets than perhaps even Kemp! Kemp, it is clear, had ambitions, as innocuous as joining the fellowship of the Royal Society but then ambitions are ambitions, and one wonders if even a man like Kemp might not be swayed into using Griffin's secrets to gain a place in the Royal Society! Wells was aware of the fact that he could not entrust Griffin's diaries to the custody of Kemp, therefore he affected a transformation in Marvel to make him perhaps the most viable custodian of Griffin's diaries.
One wonders if Wells might not be suggesting that the wisdom and maturity of a relatively less educated person like Marvel might not be a better reason for entrusting dangerous secrets than the assurance of the knowledge of a highly educated person like Kemp. The ethics of scientific research might, in fact, be better understood by the less educated and humble person like Marvel than those who are highly educated like Kemp and Griffin! Being highly educated does not condone the lack of maturity and humbleness in those who are highly educated!