Companion
Character Role Analysis
Partridge
Partridge is clearly Tom's comic sidekick. He's a nice guy, but he's kind of dumb, and he is always getting Tom into trouble with his gossip. But what makes Partridge an interesting twist on the whole sidekick schtick is that he is also a stand-in for Tom's dad. That is, Squire Allworthy believes that Partridge is Tom's dad right up until the end of the book. And Tom only finds out that Partridge is not related to him when they meet again in Book 8.
We know that Partridge isn't a proper father figure to Tom—Tom would have to respect him for that to be true—but the fact that Tom is so intimately tied to Partridge, even mistakenly, makes Partridge a reminder of Tom's mysterious origins. While Tom is off adventuring and thinking about Sophia, Partridge's presence reminds us (a) that we still don't know who Tom's real dad is, and (b) that Tom's mother is still out there somewhere. These issues of Tom's birth never stop mattering until the mystery gets solved in Book 18. Partridge is also a part of that mystery, even if he is a funny, vaguely stupid part.