An animalier, from the French, is an artist whose specialty is depicting animals. It was a particularly important art specialty before the days of photography, in much the same way as was portrait painting.
The French school produced fine painters, but is particularly known for its sculptors. The English animaliers are mostly known for drawing and painting.
In the 19th and early part of the 20th Centuries, when animal fancy was on the rise, and people had disposal income but photography was not yet within everyone's budget, fine animal artists were in high demand, and painters could earn their living from their work.