Dragon Ball Z was based on 26 volumes of the manga series
"Weekly Shonen Jump" . These volumes were turned into 291 episodes
of the show, these started showing on 26th April 1989 and finished
on 31st January 1996.
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It is both anime and manga
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the original dragon ball manga was written in 1985
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that's because there isn't. the makers of dragon ball z anime
just made it up. the original author of dragon ball z (the one who
made the manga) had nothing to do with dragon ball gt. that's why
there's no manga, just anime.