The obvious starting point is “who has made the most All-Star Games”, which, for anyone not aware, is Henry Aaron. The late Hammerin’ Hank made 25 different All-Star teams across his 23 years in the Majors, only missing in his first and final seasons. For anyone looking at those numbers for a typo, it’s worth mentioning that there were two Games per year from 1959 to 1962 (this will come up later), during which time Aaron went 8-for-8.
Stan Musial and Willie Mays also made two games all four years, which is a big part of their runner-up totals of 24 All-Star selections. The highest total for a player who couldn’t double up like that is Cal Ripken Jr., who made the Midsummer Classic in nineteen different seasons (which is still two behind Aaron and one behind Mays and Musial). Meanwhile, Mariano Rivera leads all pitchers with thirteen Games, with Tom Seaver right behind him at a dozen. Kind of a big step down there. Anyway, all of that is easy enough to find with a basic search, so let’s move on to the more complicated stuff. I’ll separate it into position players and pitchers.