49 years ago - Digger Harkness is born in the Australian Outback.
37 years ago - 12-year-old Digger runs away from home & begins working as an errand boy for criminals.
35 years ago - 14-year-old Digger finds work as a ranch hand, and first discovers his affinity for boomerangs.
30 years ago - 19-year-old Digger leaves for America, and begins working for organized crime in Central City.
23 years ago - 26-year-old Digger sleeps with Lisa Snart. He abandons her when she reveals that she is pregnant.
15 years ago - 34-year-old Digger, seeing the upsurge in costumed crime, begins wielding his signature boomerangs as Captain Boomerang. He becomes a founding member of the Rogues.
3 years ago - 46-year-old Digger finishes his term with the Suicide Squad. He seeks out his son, Owen Mercer.
2 years ago - 47-year-old Digger takes a job intended to be his last, but is killed by Jack Drake.
Of all the original Flash Villains, the thing thing that makes Boomerang stand out is the fact that he didn't become a more interesting character because of the development of the Rogues. Oh, he was on the team, but his advancement as a character actually happened before the Rogues ever existed, thanks to a certain paramilitary task force.
Originally, Captain Boomerang was just a gimmick. It actually seemed like all the Silver Age Flash villains were invented when the writer looked around the room, found an obect, and created a character that either carried it or was dressed up as it. Digger was an excuse for boomerang-themed crimes that the Flash could stop. He was Australian, because obviously, but he simply didn't need to be a more elaborate character. That didn't come about until the Suicide Squad.
Suddenly, Digger had a personality. On a team full of killers and criminals, he was the completely irredeemable one. Sexist, racist, selfish and completely unapologetic, he was the one you could always count on to say the wrong thing. He fit in well with the Squad, because by having him be such an utter jerk you got to see the other characters achieve a certain amount of nobility in comparison. Still, it wasn't exactly a characterization that lent itself to development.
Ultimately, Digger fell victim to the collective exercise in character assassination that was Identity Crisis. Frankly, he was never THAT important a character, so it didn't really hurt that much to watch him depicted as an utter failure. Plus, we got to watch the introduction of a very cool new character; Owen Mercer, the new Captain Boomerang. given that fact, it seemed okay to let Digger go.
Obviously, Digger was brought back, because of course he was. He came back in a way that totally invalidated a bunch of continuity while also killing Owen AND contradicting everything the character had ever done... basically a DC hat trick.
While the fact that he came back after dying was as dumb as ever, there was something interesting in the way this returned Digger was characterized. There was a new urgent lethality mixed into his irredeemable jerk-ness. He has a working class-atmosphere to him, a blend of utter disregard for rules, for authority.... for everything, really. Somehow the act of bringing him back had created a new personality for this longstanding character. The elements had always been there, but now they were being applied in a fresh way.
So our Digger needs to have ALWAYS been that. It actually goes a long way to explaining what makes the character stand out among the Rogues, and even sort-of explains his relationship with his son. Obviously, his time with the Suicide Squad has affected him, because afterward he goes and reconnects with his son, and manages to have the beginnings of a half-way decent relationship with him before he goes and gets himself killed. This says quite a bit about him, and he's a fun character to include.