<human>: Answer by taking a quote from the following article:

Tambo (fondly known as O. R.) was born on 27 October 1917 in the village of Nkantolo in Bizana in eastern Pondoland in what is now the Eastern Cape. His father, Mzimeni Tambo, was the son of a farmer and an assistant salesperson at a local trading store. Mzimeni had four wives and ten children, all of whom were illiterate. His mother, Mzimeni's third wife, was called Julia.

In 2004, he was voted number 31 in SABC3's Great South Africans, scoring lower than H. F. Verwoerd, before the SABC decided to cancel the final rounds of voting. The decision to cancel the results was largely informed by the fact that the majority of black South Africans did not participate in the voting, as SABC3 caters predominantly to English speakers.  In late 2005, ANC politicians announced plans to rename Johannesburg International Airport after him. The proposal was accepted and the renaming ceremony occurred on 27 October 2006. The ANC-dominated government had previously renamed Jan Smuts Airport as Johannesburg International Airport in 1994 on the grounds that South African airports should not be named after political figures.  There is a bust of O.R. Tambo at the Albert Road Recreation Ground, Muswell Hill, outside the Alexandra Park School. In June 2013, the city of Reggio Emilia (Italy) celebrated Tambo with the creation of a park dedicated to the President of the African National Congress.  Tambo's grave was declared a National Heritage site when he died but lost this status when his wife, Adelaide Tambo, died and was buried alongside him. However their grave was re-declared a National Heritage site in October 2012.  To conclude the centenary celebrations of the birth of Tambo, a commemoration was held at Regina Mundi Catholic Church in Moroka, Soweto on 27 October 2017. This same event marked also the centenary of the sinking of the troopship SS Mendi. The event was curated by Ambassador Lindiwe Mabuza and Fr Lawrence Mduduzi Ndlovu, together with the Thabo Mbeki Foundation and the Oliver and Adelaide Tambo Foundation. Participating choirs were the Imilonji kaNtu Choral Society, Johannesburg Metro Police Choir and Ekurhuleni Metro Police Choir. The soloist of the day was Sibongile Khumalo. CANNOTANSWER

What was Tambo's biggest honour?
<bot>: In late 2005, ANC politicians announced plans to rename Johannesburg International Airport after him.