Dickens created so many splendid characters that this is a very difficult question to answer. Since others have already mentioned Pip from Great Expectations, I will put in a good word for Joe Gargery from that same novel. I was recently reminded of Joe and of his relationship with Pip when I read this wonderful moment from the novel, which describes Pip learning to read and write:
One night I was sitting in the chimney corner with my slate, expending great efforts on the production of a letter to Joe. I think it must have been a full year after our hunt upon the marshes, for it was a long time after, and it was winter and a hard frost. With an alphabet on the hearth at my feet for reference, I contrived in an hour or two to print and smear this epistle:—
"MI DEER JO i OPE U R KR WITE WELL i OPE i SHAL SON B HABELL 4 2 TEEDGE U JO AN THEN WE SHORL B SO GLODD AN WEN i M PRENGTD 2 U JO WOT LARX AN BLEVE ME INF XN PIP."
There was no indispensable necessity for my communicating with Joe by letter, inasmuch as he sat beside me and we were alone. But I delivered this written communication (slate and all) with my own hand, and Joe received it as a miracle of erudition.
"I say, Pip, old chap!" cried Joe, opening his blue eyes wide, "what a scholar you are! An't you?"