Notorious ex-warlord Prince Johnson, who was filmed ordering his men to cut off the ears of dictator Samuel Doe two decades ago, has emerged as a surprising kingmaker in Liberia's presidential election.

Placing a strong third with half the polling stations tallied, the 59-year old former rebel leader looks like the man to court in a run-off election, which could prove sticky for new Nobel Peace Prize winner and incumbent president Ellen Johnson Sirleaf.

At his home in Monrovia, a large compound ringed by tall ochre walls topped with barbed wire, Johnson cuts a grandfatherly figure - far from the young general in army fatigues who took a bite out of Doe's ear before tossing it over his shoulder.

Goats and chickens roam the yard, and stone lions guard his house and a large palava hut, their teeth bared.

A large stone eagle, wings spread, is also in evidence as bodyguards, supporters and several of Johnson's 12 children mill around while he contemplates who he would support in a possible run-off.

"No, I don't want to jump the gun, no, that's my trump card, I hold my trump card," he tells AFP, laughing.

"I will decide who to support."

Despite his violent past, which also included shooting a relief worker he accused of profiteering in front of international journalists, Johnson retains huge support in iron-rich Nimba county from where he hails.

He believes his selling point is that he is an indigenous Liberian -- a sensitive issue in the country whose politics have been dominated by an Americo-Liberian elite descended from the freed US slaves who founded the country.

This, and his defence of his people against Doe, who became the country's first indigenous president after his soldiers disembowelled President William Tolbert in his bed and executed his entire cabinet on a public beach.

Doe quickly became reviled for repression, corruption and slaughter of the Gio and Mano ethnic groups.

An evangelical preacher, Johnson says he was a Christian even when he captured Samuel Doe, whose execution and the macabre home video made of it symbolised the savage brutality which marked Liberia's conflict.

"What video?" he says when asked about it, leaning forward with a piercing gaze, slightly amused, before launching into a passionate tirade peppered with religious references.

"Samuel Doe gave orders to soldiers to brutalise and gruesomely kill a president, my president" he says.

"I cannot be prosecuted, I done nothing criminal ... I fought in defence of my country, my people who were being led to the slaughterhouse like chickens and goats by the Doe regime."

The video shows Johnson seated behind a massive desk, a woman fanning him, sipping a beer while shouting orders to his soldiers to cut Doe's ears off, as the former president kneels, hands cuffed behind his back, in his underwear.

After he was finally killed Doe's body was paraded through the streets in a wheelbarrow before being displayed for several days in public.

"It is surprising because not every one of us thought Prince Johnson would be heard. At this point he becomes a key player in the race," political analyst Alvin Wright told AFP in Monrovia.

But Wright suggests neither of the finalists would shy away from making a deal with the former warlord, including Sirleaf who is a darling of the international community.

"Ellen, as president, has something that every one of these parties wants and that's that seat and in order to get that seat, if I have to negotiate with the devil to get it, then so be it ..."

Johnson expresses no regret for his past but clearly wants to put it behind him.

"There are circumstances that change people, that regenerate people, sometimes from worse to better, from the time of peace to war, I mean from a time of war to peace," he says.

"It is not hard to tell you I have changed -- it is my action that proves I've changed -- see the enormous support that I have in the country, enormous support."

Aaron Weah of the International Centre for Transitional Justice in Monrovia believes Johnson's presence in the race is a sign of impunity for many war criminals whose acts have gone unpunished.

"It is terribly wrong, people like Prince Johnson should not be given a chance to participate in public office," he told AFP.