Usually, the relationship of Principal and agent may arise in anyone of five ways, namely: – 1. By express appointment whether orally or by letter of appointment or, indeed, by a Power of Attorney, Under this heading. No formality, such as writing is required for the valid appointment of an agent except for instance, where the authority of the agent is to execute a deed on behalf of a principal. in which case, the agency itself must be created by deed. 2. By ratification of the agent’s acts by the principal. See for example Bird v. Brown (1850) 4 Exch 786, Firth v. Staines (1897) 2 QB. 70 etc. This mode of creation of agency is sometimes expressed in the maxim omnis ratihabitio retrotrahitur et mandato priori aequiparatur. 3. By virtue of the doctrine of estoppel. 4. By implication of law in the case of agency of necessity and 5. By presumption of law in the case of cohabitation.
— Iguh JSC. Vulcan Gases Limited V. Gesellschaft Fur Industries Gasverwertung A.G.(G.I.V.) ( SC.67/1995, 4th May 2001)