In the first game, he lived in a tree house in Bridge on the River Ty, but did not do much besides brag about how many Thunder Eggs he had, while recruiting Ty to do his odd jobs in exchange for them.
In the second and third games, he was revealed to be the uncle of Lily, brother of Bruce and uncle of Clarence. His wealth and influence appeared to have greatly increased as well, as he was a local leader of Burramudgee by this time (including opening the Bush Rescue HQ), and funding a variety of projects around the region.
In the second game he made souffles for some of the koala workers but they did not sound appetizing because he thinks no-meat pie is good enough for his workers and asked Ty to bring them to the Rig before the workers starve.
Night of the Quinkan
By the third game, he had become a Three-Star General during the battle with the Quinkan.
He does not feature directly in Boomerang Blast, though he does cameo as one of the civilian targets that causes the player to suffer a penalty if hit.
Dennis is like a stereotypical aristocrat: he is flamboyant, relishes leisure activities, miserly (based on being called 'Dennis the Cheapskate' by Maurie and Ty when talking to him accidentally blurted it out but then covered it up) and overall radiates an aura of sophistication. He is quite cowardly, easily scared and often afraid of the smallest inconveniences.
Despite his apparent lack of backbone, however, he became the leader of the Burramudgee community during Ty's absence during the Quinkan invasion, taking on the title of "The General." Ty was naturally surprised to see Dennis occupying such a role. As such, it can be established he does have a knack for strategy and command, despite his ridiculous demeanor.
Dennis may also possess a somewhat insane streak, as he took great pleasure in blowing things up with his rocket launcher. If nothing else, underneath that soft, aloof appearance he normally sports, he clearly takes great joy in battle. Humorously, he was intimidated by a rolling spike log more than any number of enemies.
Role in the series
As a member of Bush Rescue, he serves for The Troupe of Lightning to help fight off the evil schemes of Boss Cass and The Guild of Thunder. Though he is not the best member due to his cowardice, he is still very useful.