Conversation so far:
was Johnson elected in anything in 11th grade?
In school, Johnson was an awkward, talkative youth who was elected president of his 11th-grade class
what was the name of the church Lyndon B. Johnson's father and grandfather joined?
In his later years the grandfather became a Christadelphian; Johnson's father also joined the Christadelphian Church toward the end of his life

Question: who was johnson's grandfather?
Self-contained rewrite: who was Lyndon B. johnson's grandfather?