Cliff was a brilliant Welsh biologist and mycologist. He published a paper on DNA synthesis which the Third Doctor admired for being advanced relative to the 20th century Earth standard. He became a Nobel laureate. The two honeymooned in the Amazon while looking for obscure fungi. (TV: Planet of the Spiders) They had some "adventures" for which the locals blamed the Metebelis crystal given to Jo by the Third Doctor, so she sent it back to him. (PROSE: An Overture Too Early)