This character is the one that the author of Harry Potter tried their best to reduce screen time.
Harry Potter film underwent numerous changes compared to the books, even cutting the roles of many crucial characters. Among them is a young man whose appearance could drastically alter the outcome of the final battle in an instant.

The mysterious yet powerful character in question is Charlie Weasley - the second youngest child in the large Weasley family and the older brother of Ron. Throughout the Harry Potter film series, Charlie mostly appears through dialogue, mentioning that he is studying dragons in Romania.

In the film The Sorcerer's Stone, Ron writes a letter asking Charlie to take in the baby dragon that Hagrid had secretly raised. Additionally, Charlie's knowledge of dragons somewhat aids Harry Potter in the Triwizard Tournament in the fourth installment. Besides these details, Charlie Weasley has almost no significant role on the screen.


However, in the books, Charlie Weasley plays a crucial role, being one of the characters to be wary of. In the books, he has extensive connections outside Hogwarts and the UK, having mobilized a formidable army to join the fight against Voldemort in the climax. Without the need for direct presence, Charlie still holds a certain level of influence.

The reason behind the adjustments made by the Harry Potter film team, specifically J.K. Rowling, to minimize the involvement of Charlie Weasley in the plot. If Charlie were depicted exactly as in the story, it would undoubtedly disrupt the final battle. The forces of good would have more opportunities to suppress the antagonists, leading to a quicker resolution.
Some viewers even argue that if Charlie sent a dragon army to support Hogwarts, Voldemort's faction would be instantly 'blown away.' Charlie is likened to Harry Potter's 'Dragon Mother,' a formidable and influential character who doesn't need to be present directly on the battlefield.

Source: Screen Rant