I’ve always though Illustrators got a bum rap from the art world. If you think about it; illustrators are a throwback to the classic artists in that they’re commissioned to execute artwork for a specific use. I personally believe that illustrators as a whole are some of the most talented artists in the world as they need to not only need to be technically sound, but have to be creative and have good problem solving skills.
The two artists that immediately come to my mind are Norman Rockwell and Gil Elvgren. Both of whom were known for doing very specific things and both delivered beautiful work. Rockwell is known for his Saturday Evening Post magazine covers. He was a master with the brush and was able to capture emotion with amazing skill.
Gil Elvgren is known for his pin ups, which he did for decades. I’ve always found pin ups to be fun, but I don’t like them when they’re too gratuitous. Elvgren was always playful and suggestive, but never rude or gross. He too was a master with the brush. His textures (hair & fabric) are incredible.
These are just two of many great illustrators. The Hildebrandts, Boris Valejo and Vargas are a few others worth checking out.