Fakirs and Mystics have declared that Hoo (ھُو) is the sultan of invocations and the greatest name of Allah.

Sultan Bahoo says:

• The personal name of Allah (اَللّٰہ) has four alphabets (according to Arabic that are ال ل (ہ .  When Alif of Allah (اَللّٰہ) in Arabic is separated, it becomes Lillah  (لِلّٰہ). When the next alphabet (ل Laam) is removed, it becomes LaHoo (لَہٗ) and when again the next alphabet (ل Laam) is separated, it becomes Hoo (ھُو). All four  (اَللّٰہ،  لِلّٰہ،  لَہٗ،  ھُو)are Ism-e-Allah Zaat and Ism-e-Azam (the greatest name of Allah). (Ain-ul-Faqr)

Ibn Arabi writes in Vol II of al-Futuhat al-Makkiyya:

• Hoo (ھُو) is the final and the most elevated invocation of Mystics.

Sultan Bahoo declared Hoo (ھُو) the final and the most significant invocation:

ذاکراں را انتہا ھُو شد تمام

Explanation: Hoo (ھُو) is the final invocation of the true invokers. (Nur-ul-Huda Kalan)

• Name Allah (اَللّٰہ) includes four Divine names. Firstly, name Allah (اَللّٰہ) itself, whose invocation is the most gracious. When Alif of Allah (اَللّٰہ) in Arabic is separated, it becomes Lillah (لِلّٰہ). The invocation of Lillah (لِلّٰہ) is the Divine beneficence. When the next alphabet (ل Laam) is removed, it becomes LaHoo (لَہٗ). The invocation of LaHoo (لَہٗ) is the Divine blessing. When the next alphabet (ل Laam) is separated, it becomes Hoo (ھُو) and its invocation is the Divine favour. (Mehak-ul-Faqr Kalan)

ابتدا ’ھُو‘ انتہا ’ھُو‘ ہر کہ با ’ھُو‘ می رسد
عارفِ عرفاں شود ہر کہ با ’ھُو‘ ’ھُو‘ شود 

Explanation: Hoo (ھُو) is the beginning and the peak. Whosoever reaches it, becomes a Mystic. Being annihilated in Hoo (ھُو), he himself becomes it.

For more details see chapter ‘Sultan of Invocations’.

In the aforementioned quatrain, Sultan Bahoo has elaborated on the secrets of Hoo that are:

The seeker who obtains the contemplation of Ism-e-Allah Zaat and the invocation of Hoo (ھُو) from the perfect spiritual guide, sees Hoo (ھُو) both physically and spiritually, inside and around him when the beneficence of the spiritual guide unveils its secrets. His condition complies with the Quranic verse:

“So whichever direction you turn to, there is the Divine Countenance.” (2:115)

When the love of Hoo (ھُو) envelops the inward, it burns down the love of others and all that remains is love for Allah which enlightens it. Only Allah! Everything other than Allah is lust. Sultan Bahoo exclaims:

May I sacrifice myself upon the true seekers who remain restless and anxious to find the secrets of Hoo (ھُو) and ultimately reach their destination!