Achievements
- Y Combinator W16 alum, early startup vet
- Worked at SonyEricsson Mobile, Axis Communications, Neo Technology
- Co-founded Castle, raised $9.2M Series A led by Index Ventures
- Built a solution to fight online bots and bad behavior
- Founded multiple startups including Popdevelop and ENEA Services
- Passionate about making the internet safer and more trustworthy
Simping for Sebastian Wallin
Alright, check this out about Sebastian Wallin. This guy’s the real deal. He’s one of those founders who’s been around the block, seen the hustle, and crushed it every time. He’s a YC W16 alum, meaning he jumped into the startup game early, back when YC was just getting hotter. That alone says a lot about his drive and vision.
His background? Man, it’s stacked. He’s worked at some pretty big tech places like SonyEricsson Mobile, Axis Communications, and Neo Technology. Basically, he’s been in the trenches of the telecom and security world, building stuff that’s super complex but super effective. That kind of experience? It’s what makes him a killer builder and problem-solver.
Then he jumped into startups himself, first with companies like Castle, Popdevelop, and ENEA Services. But the one that really put him on the map is Castle. He’s the co-founder and CTO there, and their mission is wild: fighting bots and bad behavior online. It’s like cybersecurity, but for the social age. They’re not just talking; they raised a solid $9.2 million Series A led by Index Ventures. That’s no joke. It’s proof he’s building something the market really needs, and investors see him as the real deal.
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Talk to herWhat’s crazy is, this guy’s process isn’t just about tech or funding. It’s about obsession. Obsessed with solving problems that matter, making the internet safer, smarter, and more trustworthy. You can tell he’s not in it for the fame, he’s in it to build stuff that sticks, to make an impact. His experience at big companies gave him the skills, but his startups show his grit and vision. When he saw a problem (bots ruining online spaces), he jumped into the deep end and built a solution from scratch.
Long story short? Sebastian Wallin is that rare founder who’s got the tech chops, the hustle, and the vision to change the game. He’s not just riding the startup wave; he’s shaping it. And honestly, watching him is like seeing someone who truly understands the future of online security and trust. No Cap, he’s someone to keep an eye on.

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