I wonder which manga author would be the most comparable to George RR Martin's writing pace. I'd like to say the Berserk guy, but there are other hiatus mangas.
Berserk and Hunter X Hunter are the "famous" examples of manga that go on constant hiatuses.
On the shoujo side, Yami no Matsuei, much like Berserk, went on hiatus because the author was having more fun playing dating games than drawing her manga. She went on hiatus for eight years before picking up again and, although she's definitely still writing it as there's a new chapter out this month, there's been no new volumes since 2011. I can't imagine anyone still reads it, but it was a very popular manga back in the day!
On topic - Yami also has a 13 episode anime, which I watched in an entire evening at university and remember very little about except it wasn't bad for an early 00s BL show.