Not to take away from solnic's many valuable contributions to open source, but I think it would be more accurate to say he was a heavy contributor to DataMapper rather than that he wrote the majority of it
I did maintain DM for a few years, but burnt out as there wasn't enough time to keep up with the community demands and work a full time job. There were a couple of years I effectively worked 40-60 hours a week on DM and only 5-10 on work; this wasn't tenable long term and burned me out.
The small dev team, of which solnic was a core member, are an amazing group and there's no way I could've maintained DM for even a fraction of the time I did without their support.