Proxmire
We correctly think of Wisconsin as among the more liberal states in the country--it sends two interesting Democrats (Russ Feingold and Herb Kohl) to the Senate, and has a Dem governor (Jim Doyle). Yet when Proxmire was first elected to the Senate in 1957 (in a special election to replace Joe McCarthy after his death), the last Dem to have represented Wisconsin in the Senate was Paul Husting--elected in 1912. By the end of his career, Proxmire was so popular that he was routinely re-elected in campaigns that cost him less than $10,000.
By all accounts, Proxmire was a pricklish figure personally. But he was also ahead of his time in terms of philosophy--his economic restraint, social liberalism, and military-skeptical foreign policy would become far more mainstream in the Democratic Party of the 1990s than that of his day. He co-sponsored (with George McGovern) the first significant Senate amendment in the Cold War to cut Pentagon spending (in 1963); the amendment attracted four votes. By the early 1970s, though his position as chairman of the Joint Economic Committee, he had been identified by Armed Services Committee chairman John Stennis as the most dangerous Senate foe of the defense budget.
Feingold, in many ways, carries on Proxmire's traditional as a maverick Democrat, though Feingold is far more a party regular than the man who first made a name for himself--very shortly after winning election--for attacking LBJ's performance as majority leader.