Journey into Mystery was a comic that began publication in 1952 by Atlas, and although it wasn't until the eighty-third issue that Thor
even appeared in comics, let alone the title, it is most often linked
to his character. This is why after releasing the one hundred and
twenty-fifth issue of the series in 1966 that the series changed its
name to become the first volume entitled Thor.
For more than three hundred issues the title remained as Thor, but in
1996 after the five hundred and second issue of the series, they
decided to change the name back to Journey into Mystery which is what it was called up until its end in 1998 with the five hundred and twenty-first issue.
However, due to recent events, this whole chain of named, re-named and
than re-named again volumes has been brought back into light. Back in
1998, the Journey into Mystery series was ended and Thor's adventures
restarted in the first issue of Thor
and there they were contained until issue eighty-five when the series
concluded because of Avengers: Disassembled in 2004. After that event
Thor disappeared for a couple years until he returned in 2007 for his
newest volume, Thor
which only lasted for twelve issues with its restarted numbering.
After
that Marvel realized it had now published 599 comics in the
collectively-grouped "Thor" series (even though the first eighty-two issues of Journey into Mystery had
nothing to do with him they were still counted. However Journey into Mystery 503-521 was not included in the count) and therefore reverted the numbering back to
its original formation and thus, the 600th issue and the succeeding
issues were born.