The True God, the one who is truly worthy of worship.
“Or were you present when death came to Jacob and he said to his sons, 'what will you worship when I have gone?' They said, 'we will worship your Ilah, the Ilah of your forefathers - Ibrahim, Isma'il, Ishaq, one Ilah and we are Muslims having submitted to Him.'”
[al-Baqarah (2): 133]
From “Explanation to the Beautiful and Perfect Names of Allah” — Shaykh as-Sa’di (d.1376H)