Syonide is a legacy of supervillains associated with the Outsiders, specifically Black Lightning. The first two were brutal hunters and killers working for Tobias Whale and the 100. The first employed a mind control serum and an electrified whip; his successors eschewed the use of the serum. The second Syonide was responsible for the death of Violet Harper. The third was a member of Strike Force Kobra.
An earlier, unrelated character was an enemy of Wonder Woman and the Holliday Girls.
Syonide was created by Tony Isabella and Trevor von Eeden, first appearing in Black Lightning #3 (1977).
Earth-Two
Wonder Woman villain
New Earth
Outsiders villain
Other Media
Arrowverse
Syonide's replacement