The 20-year-old striker made history for the Basque side last night.
It seems like an odd phrase to say in the modern world of football, but last night saw a first for a black player at a Spanish football club.
He scored the opener, and went on to score the second goal, as Athletic drew 2-2 with Torino in the first-leg of their Europa League tie last night. In doing so, Williams became the first black player to score in the history of the Basque side.
It is quite incredible to think that this is the first time a black player has scored for the club in their 117 year history, but of course the way the San Mames club recruits players explains a lot.
The club only play players of Basque heritage. That means that only players from the Basque country - regions such as Biscay, Gipuzkoa, Alava and Navarre in Spain and Labourd, Soule and Lower Navarre in France - can play for the club and that has been the case for their entire existence.
It is a policy that has both its admirers and critics. Nonetheless it is unique, and commendable, considering the club have never been relegated from the top flight of Spanish football and continue to thrive - even in this modern world of big spending and foreign influx.
Understandably this has left them open to this issue of no black players playing for them and the potential racist connotations that go with that. Jonas Ramalho became the first black player to play for the club in 2011, over 100 years after their formation - so there is good reason to wonder about the racial barriers at a club like Bilbao.
In the past allegations of racism have been sent Bilbao's way, they have always denied them. The club's policy is simple, you must be Basque. If you are, then the colour of your skin does not matter. It is a matter of nationalism, rather than racism.
That is certainly evident in Williams.
He was born in Bilbao to a Ghanaian father and a Liberian mother. He was raised through the youth ranks in Pamplona and Bilbao. He was even given a Basque first name, Inaki - meaning fire.
He is Basque and one of Athletic's new 'Leones'. Last night, he put himself on the map and the fans of the club were delighted to see him get his first goals for the club.
At just 20-years-old Williams is set to become a long featuring member of the Bilbao first-team and the fans cannot wait to see plenty more of their now famous son.
When Williams scored yesterday he wheeled away in celebration, slapping his open palm over the Bilbao crest on his chest. The Basque country is in his heart, and the colour of his skin is therefore irrelevant to the Bilbao fans.
Long may he continue to score the goals at Bilbao.