10 Worst Things Martian Manhunter Has Ever Done
3. He Killed Manchester Black
In Season 4 of the television series, Supergirl, a Brit called Manchester Black teams up with J'onn to rescue his lover, Fiona Byrne, who was kidnapped by the anti-alien group, The Children of Liberty. After the group killed Byrne, Black stole extra-terrestrial weapons to exact his revenge against The Children of Liberty.
As Black acted more and more like a terrorist, J'onn tried to stop him, which made Black redirect his rage towards the alien. He obtained a Martian artefact called the Staff of H'ronmeer and used it to desecrate the grave of J'onn's father, making their vendetta far more personal.
When J'onn tracked him down, the British supervillain used the Staff to show a vision of J'onn's family being slaughtered by White Martians. In this moment, J'onn realised that Black would never stop tormenting him or his loved ones. Consumed by rage, J'onn grabbed the Staff of H'ronmeer and plunged it into Black's chest, absorbing his essence into the artefact.
Even though J'onn knew Black would kill thousands just to get to him, he felt like he failed himself for taking a life.