a puckish turn of mind

puckish
adjective LITERARY
liking to make jokes about other people and play harmless tricks on them:
a puckish sense of humour
a puckish grin

(from Cambridge Advanced Learner's Dictionary)

In 1948, Dr. Alpher published two papers based on research for his doctoral dissertation. The first was written with his adviser, George Gamow, a Russian-born physicist with a puckish turn of mind who obtained permission to include as a co-author Hans Bethe, an authority on the origin of cosmic elements. The authorship by Alpher, Bethe and Gamow was a scientific pun on the first letters of the Greek alphabet, which seemed appropriate for a paper on cosmic genesis.

--Ralph Alpher, 86, Expert in Work on the Big Bang, Dies