62 years ago - Jim Harper is born.
48 years ago - 14-year-old Jim becomes a junior golden gloves champion.
40 years ago - 22-year-old Jim becomes a police patrolman.
38 years ago - 24-year-old Jim becomes the adult golden gloves champion.
37 years ago - 25-year-old Jim's partner is killed. He becomes the guardian of his 11-year-old daughter Roberta.
34 years ago - 28-year-old Jim becomes the Guardian when 14-year-old Roberta is mugged.
25 years ago - 37-year-old Jim's adopted daughter, 23-year-old Roberta, has her daughter Jaime.
20 years ago - 42-year-old Jim begins working for Cadmus Labs.
15 years ago - 47-year-old Jim is killed in the line of duty. his memories are transplanted into a new, younger clone body.
4 years ago - 58-year-old Jim's 21-year-old granddaughter Jaime becomes a cop in Gotham.
2 years ago - 60-year-old Jim is nearly killed in the line of duty. he is saved by 23-year-old Jaime, and reborn in a new cloned body.
Seeing Guardian, you'd be forgiven if you guessed that he was a riff on a certain Marvel character. Guardian actually debuted in Star-Spangled Comics a year after Captain America's first appearance, they BOTH are actually copying the Shield, a character actually owned by Archie Comics. There were an abundance of comic characters that were simply guys punching people, but the Shield obviously added the titular weapon and created a whole zeitgeist of shield-wielding heroes, of which Captain America is clearly the most famous. Meanwhile, over in the pages of DC, the shield-wielding character that managed to endure to today was Guardian.
Originally, the thing that made Jim Harper stand out was the fact that he was actually the guardian of a group of juvenile delinquents called the 'Newsboy Legion'. Unpowered sidekicks were very much the name of the game back in the 40's, and he had a whole team of them. Later on it was actually the very particular genius of Jack Kirby himself that took Jim Harper and the Newsboy Legion and brought in DNA Project, which later became Project Cadmus, an organization dedicated to cloning techniques. This innovation forever tied the name Guardian with that organization and a character that was notably a little dated, a golden age police officer that decided to wear a costume and punch people, became a much more interesting concept thanks to his association with one of the more science-fictiony parts of the DC universe.
There have been a few other characters that have taken up the name Guardian. the two most notable examples are Mal Duncan, who wore the costume alongside the Titans between stints as Herald, and Jake Jordan, a completely original character based much more heavily on the original Jim Harper characterization in the pages of Grant Morrison's Seven Soldiers of Victory. It's also been recently revealed that Guardian will appear in the Supergirl TV series, and that Jimmy Olsen himself would be donning the costume.
We've actually removed the Newsboy Legion from his history, as we have with most Golden Age sidekick characters; it's just a very dating storytelling device and doesn't hold up very well. Instead, we've used the fact that his 'grand-niece' Jaime Harper had been established as a cop in the GCPD to establish that Jim was actually the legal guardian to her mother, who was in fact the daughter of his deceased partner when he was a young cop. the idea of him having been the legal guardian to SOMEONE does a good job of setting up her superhero identity before he becomes the long-time security officer to Cadmus and a clone himself. From there, we can actually follow the same story beats that have always been the basic structure of his story. He becomes a long-operating veteran to the superhero community, focused in his own little nitch of the world but always a valuable ally to other heroes. He's a building block in the house of DC, and we can use him very easily.