Dragon Ball Z features plenty of unique and powerful foes, so it makes sense that at least some of them would fade from the spot-light as more memorable enemies arrived on the scene. But the very first villain of this era of the franchise, Raditz, deserved far more attention than he actually got. Raditz is largely just a footnote in the history of Dragon Ball Z when he could have been a far more vital character to the franchise.
Raditz is the first antagonist of Dragon Ball Z. Before then, the villains of Dragon Ball were largely comedic or mystical. Even the most fearsome, like King Piccolo, were eventually contained after long battles. But Raditz brought a more cosmic-level threat with him. His power exceeded everything the franchise had seen to that point, forcing Goku and Piccolo to work together to have any chance of defeating him. But more than that, Raditz also brought a great deal of background to the series -- including the reveal that he was Goku's older brother and that both of them were members of the now-extinct race of warriors known as the Saiyans.
Raditz quickly made himself out to be a major villain for the series...but promptly died in his next battle with Goku and Piccolo. He wasn't revived at any point in the canon series and remained at best a footnote. Even his initially impressive power-level was soon made redundant by elements like the Saibamen, artificially-grown soldiers used by Vegeta and Nappa that were roughly the same power level as Raditz. Not even his status as Goku's brother ended up mattering much in the end, as Goku and Gohan weren't impacted emotionally by his loss and never made an effort to resurrect him and connect with him. Outside of the occasional flashback or cameo in the afterlife, that was the end of canon-Raditz.
Which is a shame -- at his core, Raditz has a lot of elements that could have been developed in interesting ways. His ruthless nature could have made for a fun rivalry between him and the more lax Goku. He could brought a stronger sense of drama as someone who wanted to capture Gohan and train him in the Saiyan ways Goku never knew -- setting him up as a surprisingly effective counterpoint to Piccolo. He could have eventually joined the heroes, another in a long line of enemies turned rivals learning empathy through their fights together. Or he could have stayed a genuine villain, training on his own and remaining a stark reminder of what Vegeta could have become if he didn't adjust to Earth.
There are some non-canon stories that play with the concept, proving how interesting of a proposition the idea is. In Dragon Ball Z: Kakarot, a wish granted to the player following the Frieza Saga can be used to revive Raditz. Initially believing it was Vegeta who restored him, Raditz is shocked when it turns out to be Piccolo who did it. Initially furious that Piccolo brought him back after killing him, he's somewhat humbled when (the now far more powerful) Piccolo defeats him again. The sub-story ends with Raditz accepting an offer to train with the Z-Warriors, with Piccolo's comment of Raditz always "complaining" about his losses as opposed to using them as inspiration to overcome his weaknesses, like his brother.
Another popular exploration of the "what if Raditz was good" idea comes from a what-if story conceived by Masako X -- one of the minds behind Dragon Ball Z Abridged. The extensive fan-fiction imagined a scenario where Raditz actually survived his encounter with Goku and Piccolo and ended up training alongside Piccolo and Gohan to increase his own chances of surviving the arrival of Vegeta and Nappa. This led Raditz to actually make a home with on Earth and find happiness with the Z-Warriors -- even eventually marrying Launch and having a daughter, Ranch, who became a consistent best friend to Trunks and Goten. This story and Dragon Ball Z: Kakarot both prove how effective Raditz could have been if he'd mattered in the long run instead of just being nothing more than the starter villain.
