Sparkplug, also known as Sparky, is Sari's robotic pet dog. He likes to chew on Sari's key. Transform and Roll Out! According to Professor Sumdac, he built Sparkplug as a gift for Sari on her birthday. Then, Sparkplug and Sari fight over the security key, and Sari got the key after the mutated lice scared away Sparkplug. Even though Sparkplug is Sari's pet, Bulkhead and Bumblebee first thought that Sari is Sparkplug's pet. Bulkhead questioned, "Why would a four-legged bot want a pet that big?". They probably still think that way.
He hasn't been seen much since Sari took an interest in much cooler robots. Luckily for him, Isaac still loves him, who is aware Sparkplug's novelty wore off for Sari. He is not seen in the crowd towards Soundwave when mind-controlled. Sound and Fury
He was decidedly less cute once Henry Masterson got his grubby gamer mitts on him. He becomes an evil robot drone of Henry Masterson and attacks Optimus Prime and Sentinel(without his body). The Return of the Headmaster
He is of course entirely distinct from the human miner in Professor Sumdac's employ that strongly resembles a certain otherSparkplug.