There's an ever-growing selection of Doctor Who-based graphic novels (or "comic books" if you prefer, since the term is a little controversial among comics fans).
During the 80s and 90s, only a handful were produced — but from the mid-2000s onwards, their numbers increased dramatically and have formed a constant part of the Doctor Who publishing landscape ever since.
Note: This category only lists graphic novels that have literally been published as books (i.e. with hardback or paperback-style cover/binding and an ISBN) — not magazine anthologies, of which there have been several over the years, such as 1994's The Age of Chaos and The Dalek Chronicles, which being "magazine specials" were sold on magazine shelves and without an ISBN number. Pictures of many of these "magazine specials" can be found at Tony's Trading site.
Panini, publisher of Doctor Who Magazine, have for over 15 years published a long series of graphic novels reproducing classic comic strips from Doctor Who magazine in their original black-and-white format.
Alongside their original comic series, between 2008 and 2013, IDW also published a series of "Classics" graphic novels containing colourised versions of classic 1980s & 1990s strips from Doctor Who Magazine.