The inker (sometimes credited as the finisher or embellisher or tracer) is one of the two line artists in traditional comic book production.
The penciller creates the initial drawing or sketch. Using a pen or a brush, the inker adds depth and shading to give the image more definition. Only then does the image take shape. Inking was necessary in the traditional printing process as presses could not reproduce pencilled drawings. "Inking" of text is usually handled by another specialist, the letterer, the application of colors by the colorist.
As the last hand in the production chain before the colorist, the inker has the final word on the look of the page, and can help control a story's mood, pace, and readability. A good inker can salvage shaky pencils, while a bad one can obliterate great draftsmanship and/or muddy good storytelling.
While inking can involve tracing pencil lines in a literal sense, it also requires interpreting the pencils, giving proper weight to the lines, correcting mistakes, and making other creative choices. The look of a penciler's final art can vary enormously depending on the inker. A pencil drawing can have an infinite number of shades of grey, depending on the hardness of the graphite and the pressure applied by the artist. By contrast, an ink line generally can be only solid black. Accordingly, the inker has to translate pencil shading into patterns of ink, as for example by using closely spaced parallel lines, feathering, or cross-hatching.
Some inkers will often do more than simply interpreting the pencil markings into pen and brush strokes; depending on how much detail the penciler puts into the pencil drawings, the inker might add shading or be responsible for the placement of black spaces and shadows in the final drawing. An experienced inker paired with a novice penciler might be responsible for correcting anatomical or other mistakes, modifying facial expressions, or changing or improving the artwork in a variety of other ways. Alternatively, an inker may do the basic layout of the page, give the work to another artist to do more detailed pencil work, and then ink the page himself (as Joe Simon often did when inking Jack Kirby, or when Michael T. Gilbert collaborated with penciller P. Craig Russell on the Elric of Melniboné series).