Is Asah'el among the 30?
Vilna Gaon: No. He was one of the second three, and he was a Sar over the 30. With the six (the first two sets of three), there are 36 Giborim, all Tzadikim Gemurim, like it says "Ashrei Kol Chochei Lo" (Yeshayah 30:18; the Gematriya of Lo hints to) 36 total Tzadikim in whose merit the world exists. Their merit stands for them in war. Only these were chosen among the number 1 ; the others [after this] were Giborim, but not among the number.
Malbim: Yes. Even though he was one of the second three, who brought the water, he was not with the first five, who were always with David to guard him 2 , just he was among the 30.
Why does Shmuel II, 23:39 mention 37 Giborim? And why is David, Mashi'ach Hashem, the fourth leg of the Merkavah, not among the 36?! Perhaps surely he is foremost of them; the Navi lists another 36, for shortly after this, one of them (Asah'el) died. Were not great Nevi'im, e.g. Nasan, Gad and Chushai ha'Archi, among them? Perhaps it is crucial to have 36 who go to war. This requires investigation. (PF)
I.e. Asah'el was not one of David's guards even before he was killed. Alternatively, he is not counted with the guards because he was killed before David was established to be king. (PF)
What is "Dodo"?
Radak (Shmuel II, 23:25): That was his name.
