As we know, how students success in their studying don't depend on only educational management. Actually, the characteristic of teacher is one of many things that is very important. In my opinion, the most important characteristic of teacher is active. There are 3 reasons.
First, teachers always have to study new knowledges because it makes them expert in their teaching.
Second, teachers always have to active in their teaching by preparing contents before class starts.
Third, teachers always have to make students do by themselves more than just only think because doing make them get understanding easier.
In conclusion, the characteristic that teacher in 21st century should be is active. It is based on my 3 reasons. There are always studying new knowledge, to active in teaching and making students do by themselves. That why I think active is the most important characteristic of teacher in 21st century.