Maxperson
Morkus from Orkus
Generally no. Some exceptions might exist for other background or gameplay reasons, but characters generally aren't going to spontaneously develop wizard abilities. Sorcerer, sure. Wizard, no.If an existing character, say a Fighter, decides to take a level of wizard with no prior mention of learning magic or interacting with wizards, and in a wilderness with no opportunity to find another wizard, would you let them go ahead?