How would one describe a person who is zealous about a cause?

A person who is zealous about a cause demonstrates a strong passion, eagerness, and commitment towards that cause. Being zealous indicates not just enthusiasm but also an active involvement in promoting or supporting the cause fervently. This aligns perfectly with the notion of being "enthusiastic and actively engaged." Individuals who are characterized in this manner are often seen participating in activities that promote the cause, advocating for it, and inspiring others to join in their efforts. This contrasts sharply with the other descriptions, which suggest a lack of interest or commitment, such as being disinterested, apathetic, or doubtful, which would not apply to a zealous individual.