Although The Witcher 3 protagonist Geralt isn't the most visibly (or audibly, for that matter) emotional character out there, he's still human under all that mutating and magic – and actor Doug Cockle wanted to make sure he didn't lose all of that humanity.
The legendary voice behind Geralt of Rivia explains as much in a new interview with Tom's Guide, echoing what he said back in 2018 – that he "never believed" that the protagonist "had no emotion," even if CD Projekt Red wanted him to come across that way.
At the time, Cockle didn't have any source to work from either, having not read The Witcher books or seen the Polish TV adaptation at that point. He only knew what the developers taught him about Geralt.