The activist was considered a radical for demanding immediate societal reform.

a person who advocates for fundamental or extreme changes in political, social, or economic systems
She is a radical thinker.
The group included several radicals.
He was seen as a radical.
a political radical
a social radical
the radical fringe
revolutionary
dissenter
extremist
The company decided to make radical changes to its business model.

Relating to or affecting the fundamental nature of something; extreme or thorough.
They proposed radical new ideas.
His views were considered radical.
We need radical solutions now.
radical change
radical reform
radical approach
extreme
fundamental
thorough