There are three versions of this answer. If you want the canonical answer (as in the one from the films), then they are, in order, Robert April, Christopher Pike, and James T. Kirk. Then there is the alternate universe from the 11th film, in which it goes Pike, Spock, Kirk. Then there is the non-canon explanation, taken from books and comics. That answer is given on memory-beta, the non-canon Trek wiki, as Charles Rasmussen, April, then Pike, followed then by Kirk.