Bruce Wayne might be the definitive version of the Dark Knight, but he's far from the only person to have donned the cape and cowl.
Heroes, villains, sidekicks and even bystanders have taken on the role of the Batman in the past, and with Bruce having obviously been impacted by his many years spent as the character, it's fair to say that not everyone has emerged for the better. Most, in actual fact, probably emerge worse for wear, but that doesn't make their time spent under the cowl any less interesting.
In actual fact, some of the greatest Batman stories ever told have revolved around figures other than Bruce taking on the role of the Caped Crusader. There have even been periods where Bruce has been absent from the comics for well over a year, leaving the burden to his allies to keep the spirit of Batman going in his absence.
On one hand, it's great that Bruce can depend on so many others to keep the fight going. On the other, he hasn't always been the greatest judge of character, and with the mantle leaving its fair share of scars, it's only natural that each heir has moved on from Batman to drastically different results.