The big centre-back was the very first piece in the jigsaw almost 12 months ago, having turned down the offer of a new deal at Portsmouth.
Whatmough had previously worked with Richardson at Fratton Park, with the pair enjoying League Two title success in 2016-17.
That year, Richardson and Paul Cook moved to Wigan, and Whatmough was to make the journey himself five years later.
But what did Richardson say to make Whatmough leave his Portsmouth roots for a new life in the north west?
"The first conversation I had with the gaffer last summer was simple: 'Do you want to get promoted together again?' he revealed.
"And I knew, no matter which players were coming in, with him behind us, it was something that was achievable.
"I'd been involved with a championship-winning squad with him in League Two at Portsmouth, and we had a special group.
"So I knew full well the gaffer would be putting together another special group to have a go at promotion...I just didn't know how special a group it would be!
"But yeah, having the gaffer here was a massive reason for me joining this football club.
"That's why there were never any second thoughts about making the move."
"From day one of pre-season, it was all about promotion, but we were determined to keep quiet.
"We just went under the radar, let others talk while we did our work, and we've won it."
Richardson also persuaded midfielder Tom Naylor to make the same move 12 months ago.
And Whatmough admits having his close pal alongside him has made the last 12 months even more special.
"Apparently it was mine and his fault that Portsmouth could never get promoted from League One..." he smiled, tongue firmly in cheek.
"But look at us now, we couldn't be more happy.
"It's a massive compliment to Nayls, what a player, and an even better person.
"I remember speaking with the gaffer last summer, and he asked me about Nayls.
"I got on to him as much as I could, really pushed for him to come here, and we managed to get it done.
"We come as a pair, we always have done.
"Three good years together at Portsmouth, winning the title here in our first year, and more to come.
"He'll be coming to the end of his career before me! But I've definitely got a few more years left in me."
After spending his whole career in the bottom two divisions, Whatmough - who was named in the League One 'team of the season' this term - can't wait for a crack at the second tier.
"Being in the Championship hasn't sunk in yet...it's still sinking in we're champions of League One," he added.
"It's the first time we've had a chance to reflect on such a tough season, such a tough 46 games.
"For me, this year was the Championship.
"You look at some of the teams in there...Wigan, Portsmouth, Sheffield Wednesday, Sunderland, Ipswich...loads of massive clubs.
"We all said at the beginning of the season this was sort of another Championship this year.
"And we know next year, in the real Championship, we have to raise our game another level."