This was awarded to Doron Zeilberger and myself, for our paper Rational functions certify combinatorial identities, in Baltimore, at the AMS meeting in January, 1998. To see the citations for all of the prizes awarded at this meeting, see this page at the AMS web site. Here is what Doron's department at Temple writes about his award.
My response to the award was as follows:
"I am deeply honored to receive the Leroy P. Steele Prize. I might say that doing this research was its own reward -- but it's very nice to have this one too! My thanks to the Selection Committee and to the AMS.
Each semester, after my final grades have been turned in and all is quiet, it is my habit to leave the light off in my office, leave the door closed, and sit by the window catching up on reading the stack of preprints and reprints that have arrived during the semester. That year, one of the preprints was by Zeilberger, and it was a 21st century proof of one of the major hypergeometric identities, found by computer, or more precisely, found by Zeilberger using his computer. I looked at it for a while and it slowly dawned on me that his recurrence relation would assume a self dual form if we renormalize the summation by dividing first by the right hand side. After that normalization, the basic "WZ" equation F(n+1,k)-F(n,k)=G(n,k+1)-G(n,k) appeared in the room, and its self-dual symmetrical form was very compelling. I remember feeling that I was about to connect to a parallel universe that had always existed but which had until then remained well hidden, and I was about to find out what sorts of creatures lived there. I also learned that such results emerge only after the efforts of many people have been exerted, in this case, of Sister Mary Celine Fasenmyer, Bill Gosper, Doron Zeilberger and others. Doing joint work with Doron is like working with a huge fountain of hormones - you might get stimulated to do your best or you might drown. In this case I seem to have lucked out. It was a great adventure."
Here is some P.R. that was generated.