The founder of the Organisation of African Unity (OAU) in 1963 was:

The Organisation of African Unity (OAU) was established on 25 May 1963 in Addis Ababa, Ethiopia. While the founding conference was attended by representatives of 32 independent African states and several leaders played significant roles, Kwame Nkrumah of Ghana is widely regarded as the principal ideological force behind the creation of the organisation.

Nkrumah had been the foremost advocate of pan-Africanism and continental unity since leading Ghana to independence in 1957. He consistently called for a unified African government and organised key pan-African conferences, including the All-African Peoples' Conference in Accra in 1958. His vision of a politically united Africa - articulated in works such as Africa Must Unite (1963) - provided the intellectual foundation for the OAU.

Haile Selassie of Ethiopia hosted the founding summit and served as its chairman, making him a significant figure in the OAU's creation. However, the question asks specifically about the founder - the driving visionary - rather than the host, and that role belongs to Nkrumah. Sekou Toure of Guinea and Julius Nyerere of Tanzania were influential pan-Africanists, but neither is credited as the OAU's founder in the way Nkrumah is.