The Universal Trustee, The Disposer of Affairs, The Trustworthy.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Wakeel (in Arabic: ٱلْوَكِيلُ), the one and only who can be trusted with all our affairs. He is the supreme trustee, guardian, and administrator. A believer understands the rewards of his efforts come from Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ, and therefore He entrusts his faith fully in Him.
From the root waw-kaf-lam (و ك ل), which has the following classical Arabic connotations: to appoint or entrust for the care or management of something, to have a commissioned agent, a guardian of one's interests, to rely upon, confide in, lean upon, submit to.
Who can we trust?
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Wakeel, the one to be entrusted with all of our affairs. This relationship is entirely voluntary; it is on the part of the believer to recognize that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is the authority we should trust. An authoritarian leader, a corrupt government, or an institution may try to make the people dependent on them to enforce being entrusted out of necessity. But the reality is they are deficient and clawing to hold onto power. They cannot fulfill the demands of all the people. They are limited in capacity and resources. Secondly, whether they realize it or not, their existence is finite. Only Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ existence is eternal. Therefore it would be wise for us to bring our affairs to the one who can act on them long after we're gone. Only Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ has that kind of power, longevity, and capacity. He is the only deity deserving of having all matters entrusted to Him.
Sheikh Tosun Bayrak mentions of this name, "He completes the work left to Him without leaving anything undone." People think of themselves as capable, but it is Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ who allows for everything. It's like if you were a duck floating in a pond while it's been raining, and you keep going up in the world. After some time, you think it's you and not the rain. You may say to yourself, "I must be one good duck." Realize Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ gives people specific tests of wealth and poverty or success and failure. The question in each circumstance is how will they respond to these happenings? Who will they turn to help handle their affairs?
Imam Ghazali writes, "But those so entrusted may be distinguished into one entrusted with some things (and that one is deficient) or one to whom everything is entrusted, and this is none but God - may He be praised and exalted." Only Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is trustworthy, knowledgable, and has the complete power to protect and provide the best care for His servant. Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is the all compassionate, the all powerful, the all wise. Allah is sufficient for you as a guardian, and belief and trust in this is the meaning of tawakkul. This does not excuse the need for one to provide for themselves, a true believer understands they must apply themselves to the best of their abilities. But it is Allah who decides to do what He wills and controls the outcome.
Hadith of the camel:
This concept is beautifully illustrated in the famous hadith. Anas bin Malik narrated that a man said: "O Messenger of Allah! Shall I tie it and rely (upon Allah), or leave it loose and rely (upon Allah)?" He said: "Tie it and rely (upon Allah)."  There is no need to over complicate such a simple life philosophy. Complete trust and faithfulness in Allah's plan invite peace into your life. Worldly pursuit, ambitions, and not meeting your expectations cause misery and anxiety. Acceptance frees the mind from the prison it creates.
Supplication of Prophet Muhammad ﷺ:
The name Al-Wakeel was also invoked in a du'a of Prophet Muhammad ﷺ. He recited this du'a at a time of distress, at a time when he needed His Lord to help him overcome the adversity he faced. He suffered a great loss to Abu Sufyan in the battle of Uhud. His army of 700 fought against 3000 Meccan soldiers. The losses of Uhud reported 70 Muslims were killed, whereas the fatalities of the Meccan soldiers were 22 of the 3000 soldiers. Prophet Muhammad himself was injured and bloodied in battle. You can imagine the conviction he had when he said these words. The morale among his companions was low, yet he recited these words as revealed in Surah Imran.
Allazeena qaala lahumun naasu innan naasa qad jama'oo lakum fakhshawhum fazaadahum emaananw wa qaaloo hasbunal laahu wa ni'mal wakeel
"Those to whom hypocrites said, 'Indeed, the people have gathered against you, so fear them.' But it [merely] increased them in faith, and they said, 'Sufficient for us is Allah, and [He is] the best Disposer of affairs.'" — (Qur'an 3:173)
The part of the ayat which contains the du'a has been bolded for your reference. This was also mentioned in the hadith narrated by Ibn Abbas:" 'Allah is Sufficient for us and He Is the Best Disposer of affairs,' was said by Abraham when he was thrown into the fire; and it was said by Muhammad."  Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ takes care of all those who turn to Him in their time of need. We may trust our spouse, friends, or family, but in the truest sense, they can't hold the title of being "the trustee."
Wa lillaahi maa fis samaawaati wa maa fil ard; wa kafaa billaahi Wakeelaa
" And to Allah belongs whatever is in the heavens and whatever is on the earth. And sufficient is Allah as Disposer of affairs." — (Qur'an 4:132)
Rabbul mashriqi wal maghriibi laaa ilaaha illaa Huwa fattakhizhu wakeelaa
" [He is] the Lord of the East and the West; there is no deity except Him, so take Him as Disposer of [your] affairs." — (Qur'an 73:9)
Umar bin Al-Khattab narrated that the Messenger of Allah ﷺ said: "If you were to rely upon Allah with the required reliance, then He would provide for you just as a bird is provided for, it goes out in the morning empty, and returns full." 
The believer benefits from knowing that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Wakeel. Just like the bird who goes out in search of food every day and finds its sustenance, the one who trusts in Allah's سُبْحَٰنَهُۥ وَتَعَٰلَىٰ plan will be taken care of. That's not to say there won't be any struggle. The bird still has to leave the nest in search of food - principles like the early bird getting the worm still have merit. Personal effort is a necessary precursor for change. However, the outcome of that effort is up to Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. In the Qur'an, it says, "for each one are successive [angels] before and behind him who protect him by the decree of Allah. Indeed, Allah will not change the condition of a people until they change what is in themselves." (Qur'an 13:11) It's unreasonable to expect different results if you continually repeat the same old habits. If you want to see change, you have to change. Surrender to Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ, make du'a for whatever it is you wish, and work in pursuit towards that goal.
Zaalikumul laahu Rabbukum laaa ilaaha illaa huwa khaaliqu kulli shai'in fa'budooh; wa huwa 'alaa kulli shai'inw Wakeel
"That is Allah, your Lord; there is no deity except Him, the Creator of all things, so worship Him. And He is Disposer of all things." — (Qur'an 6:102)