AK goot? Small Blind Decision

[SpeakEasy]

PokerStars No-Limit Hold'em Tourney, Big Blind is t30 (8 handed)

Weekly private tournament, $10 buy-in, 53 players started, only a few eliminated, 9 places pay. Button is Villain. Villain has been selectively aggressive, and historically plays a wider range of hands from late position. Villain has built up his stack without a single showdown. This is the 36th hand of the tournament at this table.

CO (t660)
Button (t2143)
Hero (t1495)
BB (t1140)
UTG (t1510)
UTG+1 (t1660)
MP1 (t1022)
MP2 (t1390)

Preflop: Hero is SB with A[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/spade.gif[/img].
<font color="#CC3333">UTG raises to t120</font>, <font color="#666666">5 folds</font>, Button calls t120, Hero calls t105, BB folds.

Flop: (t390) 8[img]/images/graemlins/club.gif[/img], 9[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets t150</font>, UTG calls t150, Button calls t150.

Turn: (t840) 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets t300</font>, UTG folds, <font color="#CC3333">Button raises to t1873</font>.

Hero is put all in -- why here on the turn? Hero's action?