Political teammates Weah (left) and Tubman (right) pose the only serious challenge to Ellen Johnson Sirleaf [EPA]

Winston Tubman is considered the candidate that poses the biggest threat to Ellen Johnson-Sirleaf's re-election as Liberian president after aligning himself with footbalL legend George Weah.

The nephew of Liberia’s longest serving president, William Tubman, who ran the country for 26 years, and educated at Harvard and Cambridge, Winston Tubman worked under Samuel Doe as justice minister in the 1980s.

Tubman has a long history with the UN, working at the office of Legal Affairs between 1973-1975 and from 1991-1996 and also for the UN environmental programme.

In 1998, Tubman became adviser to the Force Commander of the United Nations Iraq-Kuwait Observation Mission (UNIKOM).

Thereafter he joined the UN envoy to Somalia between 2002-2005 and participated in the 2005 presidential elections representing the National Democratic Party of Liberia (NDPL), earning fourth place.

Tubman has been criticised for moving frequently between political parties, after he changed allegiance three times between 2010 and 2011. After leaving the NDPL, Tubman became the chairman of Liberian National Union (LINU) but later joined Weah at the Congress for Democratic Change (CDC).

His association with Weah, whose rags to riches story resonates with ordinary Liberians, is widely seen as an opportunity for Tubman to leverage support from young Liberians who battle to relate to Tubman's elite American-Liberian background.

The former UN diplomat was highly critical of the awarding of the Nobel Peace Prize to Johnson Sirleaf in early October 2011 arguing that she did not deserve the prize.

Tubman's election campaign has been characterised by labelling the Sirleaf administration as a failure, alleging that the incumbent had not made substantive gains in rooting out corruption or developing the economy since winning the election in 2005.