University of Otago statistics senior lecturer Dr Matthew Parry said he delivered a talk on cosmology at the University of Cambridge 17 years ago, as a "freshly minted" PhD student.
Prof Hawking sat in the front row and after the speech was finished Dr Parry waited nervously for him to compose a question.
"Everyone knows he always asks a question. It takes him a long time to compose, and then he asks the question in a computerised voice."
Prof Hawking then began composing a follow-up question, Dr Parry said.
If it were anyone else, he might have gone to another audience member in the meantime.
"Of course, you can't do that to Stephen Hawking.
"He asked me 'how big is the universe?'," Dr Parry said. "He was just checking that I knew."
Prof Hawking died on Wednesday at the age of 76, having battled motor neurone disease since his early 20s.
His contributions to science included understanding the connections between thermodynamics, black holes and quantum mechanics. What Prof Hawking was doing was "hard enough already", Dr Parry said.
He was very impressed by the way Prof Hawking was able to do so much of the work in his head, and to communicate his research to both his colleagues and the outside world for so many years, despite his disability.
"Like any smart, busy person he probably didn't suffer fools gladly. He was very intimidating for that reason."
Dr Parry remembered sitting behind Prof Hawking at another event and watching him compose a question.
The most frequently used words came up on his computer as he typed the letter "c" - and intriguingly, just beneath "cosmology" there was "creme brulee", Dr Parry said.
Otago mathematical physicist Prof Jorg Frauendiener said while he was at the University of Oxford he had also attended events where Prof Hawking spoke, but he had never interacted with him directly.
He described Prof Hawking as a "remarkable symbol" for his field and a "very impressive" person.
He was not only a brilliant scientist but he was able to carry out his work despite being told at 21 he only had two years to live - and he did it with a "sort of showmanship" and was publicity-savvy, Prof Frauendiener said.
When he delivered lectures he was not able to put the emotion into his voice that other people would, but he did have a good sense of humour, Prof Frauendiener said.
Prof Frauendiener was impressed with Prof Hawking's final warning to the world, on the fragility of Earth and the threats facing the human race.
- By Elena McPhee
