Whiterun market-stall owners are occasionally overheard yelling at him; most notably Ysolda, who will sometimes refuse to give him money for alcohol.
If the Dragonborn helps Brenuin and he dies, a courier will give a Letter of Inheritance for 100 septims (90 septims from the Jarl's tax) to the Dragonborn, which is quite a hefty sum for a beggar.
Despite being a Redguard, when Brenuin converses with Ysolda, he states that he is a Nord. This may be an inconsistency left over from changes and adaptations across the course of the game's development.
Brenuin appears to be homeless, and is never seen sleeping; instead, he wanders around the city or loiters in the marketplace.
According to Lucia, Brenuin is the only one in Whiterun who cares for her and he got Lucia into begging; however he offers no dialogue concerning her.