The White Tiger
The original White Tiger was the first major Puerto Rican of the 70's. He was a kung-fu fightin' machine with perhaps one of the simplest costumes of all time.
He made his first appearance in "Deadly Hands of Kung Fu" magazine, but it was the Peter Parker the Spectacular Spider-Man comic series that introduced him to me. I instantly loved this guy and picked up every issue of PPTSM that had him in it. Eventually Marvel flopped out on him and had him give up the amulets that gave him the power. He drifted off into the sunset in the early 80's and such was life.
Until Marvel wanted a reboot. Rather than bring this character back and send him center stage (imagine how relevant he would be now and how cool it would have been to see him take on the Black Panther!), they opted to kill him off by being shot after being framed for murder. So this awesome hero's legacy is destroyed in his final minutes...go Marvel.
Yes, I know his death was indeed awesome and he went out with a "Yippi Ki Ya" moment most heroes would love to have...until you realize that his death was literally a five-issue gimmick with no lasting effect. He literally was dead less than 12 issues of comic continuity, making his return in the "House of M" story that immediately followed.
He died during the Avengers Disassembled storyline fighting the Kree and a hundred other baddies outside what was left of the Avenger's Mansion. A stray shot sets off one of his explosive arrows and rather than take the quiver off and throw it away he chooses to explode in a Kree mothership. Indeed a boss death and worth noting.
But it's the after-effect that I hated. I liked the character and hated to see him die. His death was really a good storytelling blow to the Avengers and Marvel Universe...but we never had time to let it register before he was back. They wasted a perfectly good death scene for this gimmick.
Ant Man (Scott Lang)
While Hank Pym was indeed the original Ant Man, the one I actually grew up reading more about was Scott Lang. He took the reins in 1979 with Marvel Premiere 47 and stayed Ant Man possibly longer than Hank Pym himself.
This was (and is) who I consider Ant Man when I look at the Bronze Age of comics. He took the character in a very cool direction, and helped out in several different titles, even becoming a member of the Fantastic Four while Reed Richards was believed dead.
Unfortunately he didn't last forever in the role. In the same storyline that killed Hawkeye we saw Scott Lang die when Jack of Hearts came back from the dead and blew him up. No purpose or reason for anything...just stupid shock value at the start of this "ground-breaking" event.