Ruff will make his Stars debut in Thursday night's visit from Thomas and the Panthers.
Ruff won 571 games -- 12th-most all-time -- in his 15 seasons in Buffalo, and another 57 in the playoffs, including a controversial Cup finals defeat to Dallas in 1999. Before bringing in the longtime coach, the Stars (22-22-4 in 2012-13) hired Jim Nill as their general manager.
Nill acquired former No. 2 overall draft pick Tyler Seguin from Boston in a seven-player deal in July that sent Loui Eriksson to the Bruins. He also signed another Cup-winning player in Sergei Gonchar, the active leader in points (775) and assists (558) among NHL defensemen
"Five years without playoffs is a long time," veteran forward Ray Whitney said. "I think the organization has made that apparent to us with the moves they've made."
Jamie Benn takes over as team captain and will try to rebound after scoring just six goals in his final 28 games last season. He finished with 12 goals in the lockout-shortened season.
"Coming into this season there have been a lot of changes," Benn said. "I want to come in and do my part and be a leader. I'm not much of a talker, but I want to be a leader on the ice."
Thomas will try to stop Benn and the Stars from getting off to a strong start in his return from a brief hiatus. The 39-year-old goaltender previously spent all eight NHL seasons in Boston and was the playoff MVP during the Bruins' title run in 2011.
The two-time Vezina Trophy winner, though, chose to sit out in 2012-13 and was traded to the New York Islanders in February. He did not play a game for that franchise and signed with Florida last Thursday.
The Panthers (15-27-6) could use his help after giving up an NHL-worst 3.54 goals per game last season while earning the fewest points (36). They allowed an average of 2.63 en route to winning their only division title in 2011-12 to end a 10-season playoff drought.
"(Thomas) brings a lot of leadership and a lot of big-game situations where we're going to need some big saves at big times," forward Kris Versteeg told the league's website. "That's a big part that a young group needs. We need big saves in big times, and that's what Timmy is going to bring."
The Panthers hope Jonathan Huberdeau can bring more scoring after an impressive rookie season. The Calder Trophy winner had 14 goals and 17 assists last season, but the offense still struggled as Florida tied Nashville for the fewest goals per game (2.27).
A rash of injuries hardly helped, and Versteeg played in only 10 games after scoring a career-best 23 goals in 2011-12. Tomas Fleischmann, though, appeared in all 48 contests and had just 12 goals after scoring 27 in his first season with the Panthers.
"I think we all pretty well know that we don't want to have another disaster like last year," general manager Dale Tallon said. "Guys are professional. They should be able to figure it out and if they don't figure it out, I'll figure it out for them."
The Panthers are facing the Stars for the first time since a 6-0 win in Dallas on Nov. 15, 2011. Florida has won in each of its last three visits.