Franz is the protagonist of the story "The Last Lesson" written by Alphonse Daudet. He is a young boy who is a student in a small town in Alsace-Lorraine, a region that was recently annexed by Germany. The character sketch of Franz is as follows:

Appearance:
- Young boy, around the age of 13
- Wears a blue smock and a cap
- Has curly hair and bright eyes

Nature and Personality:
- Curious and inquisitive
- Loves his language classes and his teacher, M. Hamel
- Initially, takes his education for granted and does not appreciate the importance of learning French
- Becomes emotional and sentimental when he realizes that it is his last French lesson and he may never have the chance to learn it again
- Shows respect and admiration for M. Hamel

Behavior and Attitude:
- Begins the story by dreading going to school and is more interested in playing outside
- Becomes attentive and focused in class when he realizes the gravity of the situation
- Feels regret for not having paid more attention in class before
- Develops a newfound appreciation for his language and culture

Conclusion:
Franz's character in "The Last Lesson" is that of a young boy who learns the value of education and his language. He is initially portrayed as careless and indifferent towards his studies but later learns the importance of preserving his culture and heritage. His transformation from a careless student to a remorseful and sentimental one is a significant aspect of the story.