Despite the club's self-imposed transfer restriction that only allows players born in the Basque Country or who developed at a Basque academy to join the first team, Los Leones have never been relegated from LaLiga.
And that tradition looks set to continue under Marcelino.
The arrival of the former Villarreal and Valencia manager at San Mames at the turn of the year has already produced an uptick in results and even an unlikely piece of silverware.
Athletic Club were crowned Supercopa de Espana winners in January, getting past Real Madrid and Barcelona on their way to the title.
The Bilbao outfit has the chance to add another two trophies to the collection this month when they compete in two Copa del Rey finals in the space of a fortnight after the 2020 decider was postponed amid the coronavirus pandemic.
First up, Marcelino's men will face local rivals Real Sociedad in the mouthwatering rescheduled final on April 3 before going head-to-head with Lionel Messi's Barcelona in the 2021 showpiece on April 17.
On joining Athletic Club midseason
“I couldn’t have imagined this situation in my wildest dream.
“When you join a team midway through the season, there are always doubts about the decision.
“I have to thank the board for choosing us to lead Athletic.
“We were fortunate to find a dressing room that welcomed us from the start and did everything they could to help us succeed.
“The results have been great which has undoubtedly made things easier."
Athletic’s unique team spirit
“A group of friends that have been together for a long time, which a huge sense of belonging is something that all the players has.
“There’s a unity and a willingness to work for Athletic and to achieve the best results possible.
“They make our job easy, they’re noble and very straightforward towards us and we’re tremendously thankful for that."
Coaching in Bilboa: Revolution or evolution?
“The club told us the reason they hired us as the coaching staff was because they felt there was a connection between how our teams played and Athletic’s philosophy."
Does Iker Muniain get the recognition he deserves?
“It’s difficult for me to about a period when I wasn’t here.
“I can make an assessment from the time I’ve been here with him and the rest of the players.
“For me, he’s an extraordinary and admirable person. The son any father would ask for.
“And, of course, he is an exceptional player, so it’s a combination of both things.
“We value a player’s personality, and he’s affectionate, warm, very competitive and a winner.
“He works hard and has that winning mentality, I’m grateful to have him.
“When me and my coaching staff arrived, he was the first person to visit our dressing room to welcome us and tell us we could count on him and the rest of the players.
“Arriving somewhere new and being greeted like that by the captain and the other players… it’s something that’s happened very few times in my career but I’m very thankful for it."
The challenges of working within the constraints of Athletic’s all-Basque policy
“When you arrive at Athletic you know what the philosophy is, so you can’t complain about it later because [the philosophy] is more clearly defined than at any other club out there.
“When you go to other clubs you have the possibility of signing players in an open market, and that can lead to disagreements when choosing a player because we don’t all have the same opinion.
“Here, a manager doesn’t get worn out in that sense.
“So, I think it’s a different challenge for us.
“Like I said during my presentation, I decided to come here because it might be the first and only chance we get to coach Athletic.
“It’s also true that I identify with Athletic's philosophy because during my playing days I was lucky enough to be part of Sporting Gijon’s academy, where academy players are used a lot.
“Then when I became a coach I continued working with youth teams and the first team.
“Each club has its own nuances, and here it’s taken to the extreme, but I identified with it and knew how it worked."
Objectives as Athletic Club's manager
“Managers live off results, especially first team managers.
“I’d be lying if I said the opposite.
“It’s different at an academy because some clubs put more importance on developing players than results.
“But at a first team it’s all about results: good results give a coaching staff credibility, and poor results normally mean you exit."