Scarlets Head Coach Nigel Davies has named Maule as vice-captain; and Thomas as stand-in captain while Maule and Rees return to fitness.
Davies said: "Matthew leads by example and is a true professional as he's shown throughout his captaincy of the Scarlets and Wales. He has a tough mental attitude, sets high standards for himself and others and has the total respect of all our players.
"It's a big plus for us that he will be back in and around our environment to give input and guidance within a squad that has a number of eager, young players looking to make their mark in the Scarlets jersey during the World Cup period while 10 of our front line players are in New Zealand.
"Gareth and Iestyn possess all the hallmark Scarlets values and impressed last season on and off the pitch with their attitude and approach. They both showed commitment in their own individual performances throughout last season, as well as contributing significantly to the group in the preparation for key games.
"Gareth is an intelligent rugby player who has grown in confidence and maturity since joining us, he has lot to give to our environment, has a good rapport with the players and provides real energy and ambition. He has progressed quickly and can set the benchmark for some of our younger players - particularly in the back line.
"Iestyn has a wealth of experience in a Scarlets shirt which will be vital in our bid to get off to a good league start," said Davies.
Matthew Rees, who is currently recovering from neck surgery undertaken two weeks ago, said it was "a real honour" to be asked to led the Scarlets again.
He said: "Obviously it has been frustrating and a big disappointment to me to miss out on leading my country at the World Cup and it's difficult to come to terms with - but the reality is there was no other option and I'm just pleased to have had the surgery now. I felt the difference as I came round, the pain in my neck eased almost straight away and the surgeon and medical team are pleased with how it went and how things are progressing now - so it's all positive."
Rees is expected to be out for 10-12 weeks with a return planned for end of October but says in the meantime he will be doing all he can around the set-up at Parc y Scarlets in the early part of the season.
Maule, who has already worn the Scarlets captain's armband last season, has impressed the coaching set-up with his mature attitude on and off the field and his commitment to the Scarlets since his move from the Dragons two years ago.
The talented centre who is expected to return at the end of September after shoulder surgery this summer said: "This is such a huge honour for me, I am so chuffed to have been asked to part of the team leading the Scarlets next season - it says a lot about the way the coaches here invest in developing the younger players on and off the field and the faith they put in individuals who are committed to Scarlets rugby and show ambition and hunger to improve.
"To work alongside two great Scarlets like Iestyn Thomas and Matthew Rees with the amount of experience they bring to the group, is a brilliant opportunity for me and I'm just looking forward to getting back on the pitch and contributing to the Scarlets' performance this season."
Thomas, who is celebrating a testimonial year in 2011/2012 said: "To be chosen to stand in for Matthew is an honour in itself and I will just focus on doing the best job I can in his absence. We need to get off to a strong start next season, the pre-season has been very positive and now we need to show the benefits of that hard work with a big performance at home starting with Aironi this weekend."