(Sanskrit ईश्वर) Literally, "able to do, prince, capable of, king, liable, queen, exposed to, god of love, Supreme Being, number eleven, supreme soul, god, ziva, ruler, one of the rudras, husband, lord, master."
"Just as air is formless and at the same time takes the form as of a cyclone, so also the formless Brahman can assume a form. [...] Ishvara or the Lord, though unmanifest Himself, caused this universe to be gradually manifested. [...] The common name of God is Brahman, Paramatman, Bhagavan or Ishvara. [...] Ishvara Himself assumes the forms of Brahma, Vishnu and Rudra through Sattva, Rajas and Tamas and becomes the creator, preserver and destroyer of the universe. [...] Anthropomorphic conception of God is that in which man gives human attributes to God. Mohammedan conception of God is anthropomorphic. The impersonal aspect (Nirakara, Nirguna) is called Brahman, or ‘unknowable’ by Herbert Spencer, ‘will’ by Schopenhauer, Absolute Noumenon by some ‘substance’ by Spinoza. The personal aspect (Sakara) of that Being is termed ‘Ishvara’ or Allah, Hari, Jehova, Father in Heaven, Buddha, Siva, etc. Just as vapour or steam is formless, so also God is formless in His unmanifested or transcendental state. He takes a form to please His devotees. He assumes a form for the pious worship of His Bhaktas. He gives Darshan to His devotees in the form in which they meditate. For a devotee who has Prema Nishtha, a form is necessary. When he develops Para Bhakti, the form will vanish away and he will become one with the all-pervading pure Consciousness. Lord Krishna is the Prema aspect of Ishvara or the Lord. Lord Siva is the wisdom aspect of Ishvara. Devi is the Sakti aspect of Ishvara. Virat is the manifested aspect of Ishvara. Hiranyagarbha is the immanent aspect of Ishvara. Hanuman is the Rudra aspect of Lord Siva. Dattatreya is the combined aspect of (Trinity) of Ishvara. Brahma is the creative aspect of Isvara. Vishnu is the preservative aspect of Ishvara. Siva is the destructive aspect of Ishvara. Meditate on any aspect you like, attain union with the Lord and cross this ocean of Samsara." - Swami Sivananda, Self-knowledge
"Really, Ishvara (the supreme master) is a very special Purusha who is exempted from sufferings, actions with results, and desires. Imagine the Universal Spirit of Life as an ocean without beaches, without shores. Think for a moment of a wave that emerges in order to get lost anew within its liquid element. Then, this diamantine wave would be Ishvara. Brahma, the ocean of the Spirit, manifests itself as Ishvara, who is the master of masters, the governor of the universe. Within Him, that omniscience (which in others only exists as a germ) becomes infinite." - Samael Aun Weor, Magic of the Runes