One assassination here, a demotion there. He is fixing his power. There is a rule in NK set by his grandfather that only his heirs are allowed power; and Un is weeding out contenders. That's also why he has silly hair BTW.
He seems to be planning to rule for longer than the other rocket man with many more rockets.
This is accurate. Kim Il-Sung, Un's grandfather and the first leader of NK since the totalitarian takeover ("Great Revolution" I think they call it), handed down a collection of ten commandments, essentially, the "Ten Principles" (NK has a constitution, but it's for display purposes only).
Number 10 is -
- We must pass down the great achievement of the revolution by Great Leader comrade Kim Il Sung from generation to generation, inheriting and completing it to the end.
Which means only descendants of Kim Il Sung can claim legitimacy to rule. Of Kim Jong-Il's three sons (Nam, Jung, Un), Nam wanted to liberalize, he's out (and murdered earlier this year, almost certainly on Un's orders), Jung is a "girly man", so he's out, so only Un could be the successor.
He keeps his hair the same way his grandfather did. With all the portraits everywhere it gives him more legitimacy as heir. (It might be some theory from something I watched or read, but it seems plausible; Why else would he have his hair like that).
This October, he demoted the last of his father’s aides, both men in their nineties. They were among around 340 people he has purged or executedKeep in mind he's only been in power for six years and he's purged 340 people in that time frame.