Journey into Mystery vol. 1 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. Although
these later Journey into Mystery issues (503-521) spin out of Thor
vol.1, they are not counted in the collective Thor series.
Back in 1998, Thor's adventures
restarted in the first issue of Thor vol. 2
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 vol. 3
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 eighty-two issues had
nothing to do with him) and therefore reverted the numbering back to its
original formation and thus, the 600th issue and the succeeding issues
were born.
In 2011, the Thor series reverted its name back to Journey Into Mystery with issue 622, tying into Fear Itself.