"Blake and Mortimer" is one of the most well-known Belgian comics series, created by Edgar P. Jacobs (1904-1987). The title is a bit of a misnomer due to phonetic issues - the titular character is, in fact, Philip Mortimer, a British scientist. He is aided by his "heterosexual life partner" (a common feature in Belgian comics at the time, and the inspiration for many a slash fanfic) capt. Francis Blake of the MI5. The book mixes detective and spy elements with fantastic concepts such as UFOs, time travel and Atlantis.
I was going to post my first contact with their books, "The Necklace Affair", but thought it best to start with the most famous story of all, "The Yellow 'M'" - the one with the most iconic cover of the series, copied by various comic book artists.( Verbosity ensues )
"Blake and Mortimer" were recently (wow, actually, about a decade ago or so) translated by Cinebook Ltd., a British company who specializes in Belgian and French comics, which gives an interesting twist to a comic set in Britain with two protagonists from Albion.