A person who habitually seeks to harm or intimidate those whom they perceive as vulnerable.
Seek to harm, intimidate, or coerce (someone perceived as vulnerable)
Mid 16th century: probably from Middle Dutch boele ‘lover’. Original use was as a term of endearment applied to either sex; it later became a familiar form of address to a male friend. The current sense dates from the late 17th century.
Joe was a bully. That’s all there is to say.