Can a leader also be a follower?

Of course he/she can. Leader can follow the ones, who were before him/her in that place, respects them and see them as their role models. Leader can also be a follower of other organizations who serve him as an example that he strives to accomplish. That is good for possible cooperation between different organizations which always lead to better results regarding society improvements. Ultimately, he/she may be a follower of his followers, which is also desirable because he needs to listen to their advice, work closely with them, receive their help, motivate them to work and direct them.