It was, Ruddock believes, the best decision he has made in 18 months as Wales boss because Thomas has been a revelation.
Thomas led Wales to a first Grand Slam in 27 years, he won the European Cup with Toulouse and, after being selected for the British & Irish Lions, he ended up as captain for two Test matches.
"I could not have won more if I had wanted to! It was just unbelievable," he recalls.
Thomas demanded silence for his first team-talk as Lions captain and then warned: "We lost the first Test because they hated us more than we hated them.
"That must never happen again - not ever. Thank you."
And with that he walked off. The Lions lost, but it was in spite of Thomas' inspirational captaincy, not because of it.
Thomas was the unifying force that inspired Wales to the Grand Slam. He is playing the best rugby of his career at present, but even when he was sidelined halfway through the championship with a fractured hand, Thomas' role in Wales' success was crucial.
"Gareth has an incredible influence on the team," said Ruddock. "He has great courage and honesty.
"He has a perpetual excitement about playing for Wales and he makes everyone realise how special it is to represent your country. He has won loads of caps, but he wants to play for Wales as much as ever and that enthusiasm rubs off on the rest.
"He did an excellent job for the Lions and to some degree his achievements on that tour were even greater than they had been for Wales last season.
"We had been winning but the Lions were on the floor after the first Test and he picked them up through the sheer force of his personality."
Thomas' incredible year ended with a first Wales victory over Australia since Paul Thorburn clinched third place in the 1987 World Cup.
But despite all the success and adulation, Thomas is hungry for more. He wants Wales to once again take their place on the top table of world rugby. He cannot bear the idea of 2005 being seen as a one-off.
That 24-22 victory over Australia came on the back of three poor performances.
Wales were beaten heavily by New Zealand and South Africa and scraped a win over Fiji.
Injuries had depleted the side, but Thomas bound them together tightly and a new unit emerged, a unit that proved too strong for the Wallabies.
Thomas is now determined to carry that confidence, that spirit and that momentum into the Six Nations and a crucial opening game against England at Twickenham.
"We can't afford to come in rusty. We realise we can't come into the Six Nations like we came into the autumn," he said.
"We are champions, deservedly so, and we have to go out and play as favourites.
"Australia was a big step forward, we did what a lot of other Welsh teams have not done and beat a Tri-Nations side.
"Our confidence is on a roll ahead of the Six Nations. England at Twickenham first up is a massive game - and we will be hitting the ground running."