One of the first players that comes to mind for me is Jacin Sinclair - former Balmain, Souths and Easts outside back in the 90's. Before posting this I google-searched the spelling of his name and was a bit shocked to find that he actually died late last year (see below link) and that he was only 38.
He should've been bowing out of the NRL only a few years back yet he wasted his talent to an extent that he exited the RL scene clearly well before his time.