Almighty AA

My first thought here is that he got there on the turn. Like you, in the tourneys I play river raise bluffs, especially on a brick, are invariably value hands. As such I am inclined to fold here. We have under-repped our hand to an extent so I suppose its not out of the question that he is raising for value with a hand worse than ours.

Could he be jamming a missed draw? Possibly, but I just don't see it often in my games.

When you check the turn you cap your range (not criticizing the check, just pointing that out). So it's a spot where on a blank 4 river AA is pretty much the top of your range, which makes betting the river in position and reopening the action a risky play. Again I'm not criticizing as I would have also bet if I took your line, but recognize you are mostly capped.

On the river, given your description of villain it seems like they can definitely show up with some bluffs. Given that you bet so small on the flop and checked back turn, he's arriving to the river with a fairly wide range that includes plenty of Jx (draws that turned a pair), 9x, even 6x, stuff like pocket 8s and 7s, etc. that have some perceived showdown value but could realize they're not good and bluff raise all in after you bet river. He also has plenty of 2 pair + value hands, and you've got to ask yourself how many of those check river after you check back turn? I would imagine many of those combos bet river themselves, which COULD weight his river jam more towards bluffs, but that is an assumption.

Ultimately river is a player dependent spot and it mostly just comes down to whether they are over or under bluffing. I would fold against many opponents but given your description of opponent as a maniac I probably call.

FWIW, a few other notes:

On the flop, I would have bet a bit bigger. I'm not saying you need to go huge but I like at least a 1/3 pot bet. Your 1/4 pot bet makes it an easy float with any pair and/or gutshot + BDFD type hand, of which there are many, and most turns are going to be scare cards. A bigger bet puts a lot more of his range in a difficult position where he is more likely to make mistakes.

On the turn i would have considered betting again and keeping your range uncapped while you charge all the many pair + draw type hands.

Overall though I think you played the hand fine. If you called and he had it this time I wouldn't beat yourself up.

Pf size good
Range him as pp, sc, Axs, suited paint after the open/call ie standard GTO 50bb range. You weed out the dregs but v is still wide here post.
Size up a little on the flop for value
Prefer bet/fold turn but check is fine
Check river

early stages of a super long mtt with significant sdv against a suspected nutter. Huge fan of thin river value but not here.

Against a guy who's been in 5+ all-in pots and is clearly spewing off a stack he ran up, the river jam is going to be heavily weighted toward value in most lineups but this villain sounds like he's capable of turning a missed flush draw into a shove. Checking back the turn is fine given how the board ran out and how your line looks, but it does set up this exact spot where he can rep a ton. I've faced this spot maybe a dozen times over my career and the read on the specific player almost always has to be the deciding factor. With this guy's history at the table I'm probably putting chips in.

Hmm you can go bigger pre if villian is really spazzy. Maybe 21 or 24k but idk 18 is prolly ideal. I kinda like to size up in certain button spots bc I’m going to be fairly light at times with hands such as A5suited, k9 suited, some other light stuff but 18 is normally fine.

I would bet flop a tad bigger. Maybe like 1/2 pot. I consider 1/4 pot way too small in this spot if we trying to get stacks in. Would be more fan of that sizing if it was a 4 bet pot. Board has draw potential also so really don’t want to let villian off the hook calling draws for cheap.

I would bet turn. Checking turn seems really blah. Maybe with a plan to check river bc you almost never called by worse.

As played, idk maybe fold. I’m bad so I prolly wouldn’t fold but this spot seems super underbluffed. X raising river seems like value value value.

In the past couple of years I have won hands with AA but smallish pots because I have bet larger on the flop than here and then when I am ahead and bet the turn as well they fold. There have been times where my turn bet has to be a jam because of the overall sizing preflop and on the flop. And in those spots my opponent typically folds with a worse hand when I have bet large on the flop. There have also been times this year when my opponent has flopped a set and has just called my flop and turn bets.

Recently I did this kind of small flop sizing against JJ on a T75 board and he obviously called (in position as I was SB that hand). The turn was an 8 and when I turn jammed he tank called and I had an 86% chance of having a monster stack and going deep (we were about 20 people from the money on Day 1 of a 3 day tournament). Now he did hit a J on the river but I was very happy he called and I think he did call because of my flop sizing which made the possibility of being called on my turn jam very likely.

Here if I bet 18,000 on the flop there would be about 77,000 in the pot if he called and I would have like 94,000 chips. So on the turn I would either have to jam or bet smallish like 20,000 or 25,000. I didn't like either of those options.

I didn't want to bet this turn because if I do and am called I am often behind. This happened OOP with AA on a T73 flop vs TT and he just called, then called the 9 turn bet and jammed the river after my bet and I had to call because there was so much in the pot.

Here if I bet about 25,000 on the turn and am called there would be over 100,000 in the pot and I would have like 80,000 left. So the river would be dicey if he led out. Especially if he jammed. Here by checking I am making it obvious I don't have much and I expected a lot of river leads outs from Villain as bluffs or value bets some of which I could be ahead of (like AQ/KQ/QTs). I also thought that if he checked the river it would mean he didn't have a monster like a straight (KTs/T8s) or a set or two pair like QJs.

I thought his unpaired hands would be AXs where he was either on a FD or BDFD or it could be some SC like T8s/KTs/87s/86s/76s (there was a 5 on the flop not a 6 that was a typo...) He was opening wide.

My thoughts about Villain going to the flop were either he had a very big hand like AQ/QQ/JJ that he was thinking of 4 betting preflop OOP or he had a smaller PP or SC or some broadway hands like KQo/KJo/QJo where he was thinking about folding preflop.

Because he was so wild aggro I knew he could have any of those hands. And in fact he did. He had 55. He had flopped a set and for a reason that I did not see coming he checked the river when I had basically indicated I had nothing or a pair worse than Qx.

I don't get why he did what he did since I was most likely going to check back the river. But maybe his thinking was that he wanted me to bluff and then he would at least make that much by checking. Then when he jammed I would almost always fold but so what at least he would get an extra 25,000 or so. My thinking was that he would lead out the river large, like pot sized or a little bigger to make it look like he was possibly bluffing because he had jammed so many times before. And he could even have jammed at a little less than 2x pot.

As was mentioned by a lot of people, his river c/r jam is almost always a very strong hand. Even though he had been jamming and bluffing a lot. I think if I hadn't won that other huge river jam at Planet Hollywood where I had a nut flush on an AAxxx paired board against another wild aggro overbetting guy, I likely would have folded here.

My other thought is that I had a subconscious premonition on the flop that Villain had flopped a set. And it never came to my consciousness. So while I played it like I knew he had flopped a monster I ended up taking into consideration that he had been a very wild aggro river jammer.