What made Zaheer so powerful before he got bending?

I mean they said before he was a bender he was still one of the most dangerous people on earth. Now I know their have been plenty of non benders who could take on benders(the blue spirit, master piando), but a guy that was so dangerous that they lockded up hundreds of feet high away from everyone else?

The Red Lotus' plot was to kidnap Korra in her infancy and make her their own Avatar to shape the world in the image they wanted, Winter-Soldier style. Obviously enough, Zaheer was supposed to be her air-bending master. Plus, he was their de-facto leader.

Ummm. No they wanted to kidnap Korra in order to murder her in the Avatar State and end the line of Avatars. Zaheer also was not an airbending master until after Harmonic Convergence....right before he escaped.

Zaheer was already heavily invested in the Airbender philosophy, having great admiration towards their culture and ideals (ignoring the whole pacifism part) leading to great understanding of their mentality. All bending is performed with different martial art movements, making the motions for bending useful regardless of whether one could bend. My thoughts are that as Zaheer was an admirer of the Air Nomads, he based and developed a formidable fighting style around the airbending motions, which later lent him a great levels of skill when becoming a bender during the Harmonic Convergence. Not quite to Tenzin's caliber but enough to become a formidable opponent.

I finished watching Korra very recently, and Zaheer did state that the Red Lotus intended to kidnap her in order to create an Avatar (presumably to suit their needs) with each of the Red Lotus members intended to be her varied teachers. Arguably, despite not being an airbender it could potentially be seen that Zaheer would still teach her the theology and motions of airbending due to his understanding. Obviously this became an impossibility once Tenzin and Tonraq had allowed her to develop her own ideals, so they instead chose to execute her as they could no longer use her.

@lunacyde: Well they said they wanted to kidnap her as an infant and teach her their ideals right? Didn't they just choose to murder her and end the avatar line as plan B once she resisted that?

He was not a dangerous combatant. He was a dangeous person. He was greatly gifted tactical ability-wise, and he was helped by a group of deadly master benders. His plan was to kidnap the Avatar and turn her evil. Obviously he had martial arts training before he got bending but that doesn't make him any better than your average nonbenders.

And Tonraq already beat him before he got airbending... Not that dangerous.

I think Zaheer used to be one of the strongest non benders in the world.

Creators confirmed that he was a highly skilled martial artist in an interview, before he got his bending powers.

"Ever since Zaheer escaped prison, us avatar fans have long since speculated why Zaheer was able to grasp air bending so quickly despite only recently developing air bending abilities.

The Creators explain that Zaheer was a master martial artist before he got air bending. Bryan says that 'in real life, any weapon is meant to be an extension of your own body'. He also says 'If someone is truly a master of martial arts, if you hand them a broom, a sword or a stapler, he or she should be able to use that expertly because they in such control of their body' 'Zaheer was always meant to be a hardcore shudo catch wrestling master' Bryan says

He then goes on to say that the idea was that when Zaheer awoke with air bending, he was practicing in his cell for a time before he escaped. They also state that he was already a high level spiritual person who had masters high advance spiritual abilities."

The reason he was able to air-bend so competently was because he was already trained in the fighting style, and as TLA showed, a skilled non-bending can go a long way.