Board Thread:Wiki/@comment-5774380-20161108134217/@comment-26495049-20161109233906

GodKingReiss wrote: What do you think Kruger's motives are?


 * He was ready to let Grisha die, but changed his mind.


 * He wants to join Grisha in his goal to obtain the Founding Titan.


 * He wants to give Grisha his Titan power and send him in alone to obtain the Founding Titan.


 * He wants to join Grisha and head for the safety of the walls.

I think Kruger was waiting to choose his successor, otherwise why would he wait for this moment to reveal himself? The parts where it cut to Kruger's face after Grisha said something that touched his heart seemed to imply that he was slowly being convinced that Grisha was the right person to carry the torch for the Eldians.
 * He has a different motive.