'Fido' comes from Latin (literally 'I trust'). This article from a psychology magazine goes into more detail about its popularity as a generic name for a pet dog.

In short, the author claims that the popularity of the name in modern psyche comes from the name of one of Abraham Lincoln's pet dogs.

https://www.psychologytoday.com/blog/canine-corner/201110/why-are-dogs-so-frequently-called-fido