I think we'll start this little series with my Welshest character: Bleddyn Ellis.
He was born and raised in Gwalchmai, which is village that's smack in the middle of nowhere on Ynys Môn, having been born in a farmhouse just outside the village itself. The island, like most of North Western Wales, is a very very low-income, Working-class area - his specific area is very agriculture-heavy because of its very rural location... His mother was a homemaker and part-time laundress, while his father was a quarryman who worked at Dinorwig quarry and would often leave the home for weeks at a time, sending a good portion of his pittance of a wage back to the family on the island via the post.
Both his parents were Welsh and spoke very little English, which means he grew up mostly speaking his native language of Welsh at home and with most people he came across while growing up. He didn't learn English until he was in his third year at primary school (around 7/8 years old) and didn't fully gain the ability to code-switch his heavy North Western Welsh accent until he was about 22 and he'd been living in London for four years.
He is a very proud Welshman, making a point of saying so whenever he gets the chance -- especially when he's in discussion about his writing work. Though his most popular/famous writing is in English, he does have work published in his native Welsh including a book of poems entitled: Beth Am Yr Ysbryd? (What Of The Spirit?) which is full of poems he wrote about his time living in London and feeling like a fish out of water, and a three separate novels entitled: Hunllef (Nightmare) which is a horror novel, Fasiwn Stâd (lit.: Estate Fashion, contextually: What A State) which is a 'slice of life' novel, and Malu'n Racs (Broken (Into Pieces)) which is a dramedy-romance novel -- he will bring them up whenever an interviewer asks about his first English book and refers to it as his first ever book because it isn't, his first ever published book is BAYY?.
Blaidd is a regular competitor at the Eisteddfod, usually submitting his poems and prose by post, and has won a total of 2 chairs. He has mixed feelings about the festival, given that it tends to favour Southern Welsh people and/or people of higher class than Bleddyn is/was growing up (ie: people with a lot of money). He has also recited his Welsh poems at various writing events across the UK (not that they got much praise outside of his homeland).
His all-time favourite (Welsh) bands are (Yr) Anrhefn and Datblygu, and he often listens to them for inspiration. He has successfully gotten his non-Welsh friends into both... Mostly by accident.
He has made a point of speaking Welsh to his daughter, Begw, in a bid to keep the language alive and to teach her about her heritage. He believes that it's important for her to learn the 'mamiaith' so that she can have easier access to her history, culture, and be able to communicate with family on the Ellis side of her family tree. In doing that, though, he's gotten ire from English parents and he's found his (reluctant) respect for English people slip more in recent years because of how he's been treated for the great sin of speaking to his child in a language that's more natural to him.
Bleddyn was alive for a lot of the more recent-memory Welsh history, such as the drowning of Tryweryn, Cymdeithas Yr Iaith protests, the arson attacks on English-owned summer homes in tourist-heavy areas/areas of dire housing crisis due to tourism, and is pro-devolution (or pro-a Welsh Assembly, which is now known as the Senedd/Welsh Government -- something that operates separately from the UK Government in a majority of areas, including (minor) law-making, international relations, health, education, etc. and came to be in September of 1997, Blaidd's story is set between January 1997 and September 1997) & pro-independence. He wants to see a free Wales at some point in the future, but currently settles for openly talking about his culture and using his language so as to be sure it won't be lost to time.