mainstay

(noun) a prominent supporter. Synonyms: pillar. Example: "He is a pillar of the community."

(noun) a central cohesive source of support and stability. Synonyms: anchor, keystone, backbone, linchpin, lynchpin. Examples: "Faith is his anchor." "The keystone of campaign reform was the ban on soft money." "He is the linchpin of this firm."

(noun) the forestay that braces the mainmast.