An artist with the help of certain digital tools.
Usually, these programs are either vector based or raster based software. Vector based software involves storage of content digitally based on mathematical axioms. It has an advantageous property of being scalable. Hence, any drawing made using this software can be very easily enlarged without being concerned about the grade of illustration. Such graphics can be easily downloaded from the internet and can be edited to incorporate in some other projects. These are usually known as drawing programs.
Raster based software are responsible for creating images from pixels. These pixels are small rectangular units which collectively create an image on the screen. But these are not scalable. Hence, if you change its size, there can be an impact on the quality of the picture. These are usually known as painting programs. An image created will have a different look and feel in raster based software if compared to the same image created using vector based software.