Some traditions identify familiar spirits who aid witches and warlocks (among others) to practice their craft. Usually, these helpers take the form of an animal. In Europe this was often a black cat. Familiars in Fantastic America and Midwestern Magicians do not follow this pattern exactly.
Familiars in the Magic Unleashed series are people with an affinity to magic but who are unable to perform spellwork. Instead, familiars are inexorably drawn to wizards with whom their affinity aligns. Each school or kind of magic has a ritual to empower familiars. This also links them to the wizard they will serve. Familiars are not slaves, they retain free will, and can break the link to their wizard.
Life wizards create paladins, fierce protectors of life. Aqueous wizards create tritons, fast swimmers of the deep. Earth wizards create beastmasters, who link with and empower animals to aid their cause. Necromancers create minions, cold and dark enforcers. Chaos wizards create hellions, infernally strong disciples of destruction. Sorcerers create apprentices, their electrically charged defenders.
Arcanists use practical magic. They do not create familiars, but they do sometimes adopt a totem animal that embodies characteristics they admire. The fox for its cunning, the owl for its wisdom, the raven for its intelligence, or the smart and lucky rabbit. These animals are all smaller and hardly menacing but can still outsmart and defeat their adversaries.
There is one other type of familiar that may account for some traditions associating animals with the role of helper. Animals from other realities are, in general, ill suited to life on Earth. Animals stranded here will seek out a wizard attuned to their home, if one is nearby. A wizard can help these animals survive if it is at all possible. In return, the animal can aid the wizard or simply keep them company as an exotic pet.