I could be way off here, but could this be the very first time a famous cartoonist appeared as a product endorser? And what a product to endorse — one of the patent medicines of the day! I’m not familiar with Paine’s Celery Tonic in particular, but you can bet that this tonic was mostly alcohol, as were most of them. Might even have been a cocaine product. You can read about this and other snake oil products here.
As you can read in the ad, Bernard Gillam was a part-owner and chief cartoonist for the weekly humor and political comment magazine Judge.