[crockpot]

i think you have to call given the range of hands you put him on. if he will do this with any hands weaker than KK, you have a call since there is already some money in the pot.

further, he might just be trying to get it all in so you can't force him out later with a bet when you have position, or he thinks since you are raising so much, you may be pushing the action with something worse than his Ax. he may have aces, but he is quite likely to flip something that you have beat too.