The culture was already there when I joined the team, 8 years ago - but for me, it started with the on-boarding process when someone new was hired. They were introduced via email to everyone, including a short bio. Everyone else responded in kind, so your first week was already a lot of informal conversations getting to know everyone. Then it just continued - we'd all help new folks get up to speed, ask them how things were going... it felt natural from day one.