He leaves on a high note, having taken his party to a position of real power in the minority Gillard Government. The defining policy of Ms. Gillard's tenure thus far, the carbon tax, is a direct result of the Greens' influence. Bob Brown did, at least in this instance, completely out-negotiate the so-called 'great negotiator'.
But what of the Greens' fate now, in the aftermath of their founder's departure? Dr. Brown was a savvy and talented politician. His successor, Christine Milne, is not in the same class, and she struggles to present herself so endearingly to the public.
Waiting in the wings are two ambitious Senators who represent the next stage in the Greens' evolution. Sarah Hanson-Young and Lee Rhiannon are a different political breed to Dr. Brown and his former deputy - while environmentalism has been at the heart of the Greens' philosophy thus far, for this next generation of leaders it plays only a complementary role in a wider platform of economic socialism.
There is a real risk that Bob Brown's exit will presage the waning of his party's power, much in the same manner as Cheryl Kernot's departure doomed the Democrats.
The Greens must now fight internally to remain the unthreatening environmental party that was exemplified by Dr. Brown's public image. The extremism of Senators Hanson-Young and Rhiannon can only hurt the party's cause in the future.