Brooks was a resident of the town of Blackwater in 1899.
Events of Red Dead Redemption 2
Arthur Morgan encounters Jimmy Brooks in Valentine, where he recognizes Morgan as having been in Blackwater with the Van der Linde gang, during the botched ferry robbery. Arthur attempts to convince him otherwise, but Brooks rides off in fear. Morgan chases him across the country on his horse until Brooks falls off his own and is left hanging off a cliff, begging to be saved. Arthur then has the choice of either saving Jimmy or letting him die:
If Arthur chooses to kill him: Not wishing to take any chances with him, Arthur ensures that Jimmy won’t say a word by stamping on his hands and thus causing him to plummet to his death. For this, the player will lose Honor.
If Arthur chooses to rescue him: After helping Jimmy up from the cliff, Arthur threatens him into not saying a word about the fact that he was in Blackwater. Brooks is extremely grateful for his life being saved and promises that he will not tell anyone, before giving Arthur a steel pen and then riding away. For this, the player will gain Honor. Jimmy's final words to Arthur can be one of the lines he reflects upon during his last ride.