Several important solar deities are generally thought of as the children or lesser parts of Yelm, said to be created when Yelm was murdered by Orlanth. The God Learners called such entities “srvuali” – emanations of a Rune with a narrower definition but usually more approachable.
Probably the most important of these “parts of Yelm” cults is Yelmalio.
People have a tendency to treat Greg’s deep background notes from the Dawn Age as a snapshot as to how people understand those cults some fifteen centuries later.
Note that GRoY is set a long time ago. If you read Fortunate Succession you can see that these cults change a lot over the centuries. In about the same time Amun-Re became Zeus.