Well, Kirby worked for Timely/Marvel up till 1942, when he and Joe Simon were fired because they were secretly working for DC at the same time. Another version (in the above video) is that Marvel fired Simon & Kirby to get out of paying them huge monthly royalties for CAPTAIN AMERICA COMICS, that was selling over a million issues per month.
At DC from 1942-1946, Simon & Kirby did Newsboy Legion, Boy Commandos, Sandman, and Manhunter. I'm not exactly sure of the reason they left, but right after leaving Simon & Kirby co-created Hillman comics, created the first romance comic that was highly successful, as well as horror comics like BLACK MAGIC, and crime comics like JUSTICE TRAPS THE GUILTY.
When Hillman folded around the time the comics code began, Kirby mostly worked after for DC, until his clash with Jack Schiff over the "Skymasters" newspaper comic strip, circa 1958, where Kirby apparently shorted editor/business-negotiator Schiff in a collaborative "Skymasters" comic strip venture (a court ruled damages in Schiff's favor), and Kirby either didn't want to work for DC after that or was blacklisted. The very day Jack Schiff retired from DC in 1970, Kirby contacted Carmine infantino and worked out a contract to leave Marvel for DC.
In between 1955-1962, Kirby struggled and did brief jobs for Gilberton (Classics Illustrated), Harvey and other publishers, but without DC or another decent-paying publisher, Kirby apparently went crawling back to Marvel at a time they were on the verge of going out of business (late 1958), and resurrected Marvel into an incredible giant in the field.
As we discussed previously both Alan Moore (still living) and Jack Kirby (his estate) are each worth about $10 million, so it's difficult to feel too sorry for either of these guys. Could they have been given a fairer deal with a larger slice of the pie? Sure, absolutely. But 10 million a piece is no small sum.
