Fred C. Dobbs in "Treasure of the Sierra Madre"
 

Some people say that Dobbs would have been just fine back in a big American city, where he could put his money in a bank. But Dobbs's problem was obviously decreased serotoninergic neurotransmission.

Had Dobbs had a higher concentration of serotonin in his synapses with lower rates of reuptake, he wouldn't have gone batty with paranoia & delusional thinking, & he, Tim Holt & Walter Huston would have remained pretty good friends.

Then again, maybe not. :p