I'm the perfect age I think to have affection for Doctor Strange's brief masked period. The character was being illustrated to magnificent effect by Gene Colan and Tom Palmer with scripts by Roy Thomas.
But after being split off from SHIELD and taking on the numbering of the venerable Strange Tales title, the sales must have slackened (or were never there) as Strange got a makeover. Ostensibly Ditko's mage was not the type of character it seemed that Marvel was having success in promoting, so they juiced up his superhero props by giving him a sleeker costume and an eerie blue mask. There was some gobbledy-good story reason, but it was done essentially to spike sales.
The look even slipped into an issue of Not Brand Echh.
I liked it, but it didn't work all that well and a few issues later Doc got the axe.
When he popped up later in Sub-Mariner and the Hulk he had the new look but gave up sorcery until the advent of Marvel Feature #1 and the debut of The Defenders. The story had Mordo pretending to be Strange so to make such trickery less easy (I'm not quite sure how but it was an excuse) Doc took back his vintage look, and the mask was put away.
It's shown up a few times since, in some Doc runs. But it made a big return in The Order, the book that brought back the Defenders for a short time. Later still Doc took on the superhero suit in some issues of the Hulk.
Third Eye liked the Doc look it seems as they made some really superb black light posters from Colan and Palmer pages.
And here are some Colan originals showing the masked Doc.
I know some folks hate it, but I adore this now-classic and mildly malevolent variation on Marvel's magician.