(The Holder of Supreme Authority)
The Governor, The Ruler.
Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Waali (in Arabic: ٱلْوَالِي), The One who is the sole planner and governor of all things. He is fully supportive, helpful, and a master of all. He manages and disposes of things at His will based on His judgment.
From the root waw-lam-ya (و ل ي), which has the following classical Arabic connotations: to be near, close, nearby to be a friend, helper, supporter, maintainer, to defend, guard (lit. friendly dealing), to be in charge, to turn one toward something, to be the master, owner, lord.
Among the disputed names:
As we've mentioned in previous names, different scholars have different criteria for what qualifies as a name of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ. Of the 99 names, 81 are explicitly mentioned in the Qur'an. Therefore, there isn't one agreed-upon list for the remaining 18 names. Al-Wali is one of those names that is deduced and, therefore, not included on the list of certain scholars. This includes Ibn Mandah, Ibn Hazm, and Ibn Hajar, among others. However, others, such as Imam al-Bayhaqi and Imam al-Ghazali, have included this name in their lists. Note as an attribute to describe Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ it is valid.
To be a ruler...
This name is also not to be confused with one we've already discussed in Al-Waliyy (ٱلْوَلِيُّ) - The Protecting Associate. Here Al-Wali (ٱلْوَالِي) refers to being the ruler or guardian, and this encompasses three qualities. Imam Ghazali mentions that being a governor requires organization, power, and action. Failure in any of these respects relinquishes the title of being called the true ruler.
Below are just a few verses that mention Allah's complete dominion. It demonstrates how He is the best planner, the all-powerful king, and the one who manages the affairs of all things.
From the Qur'an:
There are no direct mentions of the name Al-Wali, but we can understand this attribute further by verses that describe this quality from the Qur'an.
Wa iz yamkuru bikal lazeena kafaroo liyusbitooka aw yaqtulooka aw yukhrijook; wa yamkuroona wa yamkurul laahu wallaahu khairul maakireen
"And [remember, O Muhammad], when those who disbelieved plotted against you to restrain you or kill you or evict you [from Makkah]. But they plan, and Allah plans. And Allah is the best of planners." — (Qur'an 8:30)
Qulil laahumma Maalikal Mulki tu’til mulka man tashaaa’u wa tanzi’ul mulka mimman tashhaaa’u wa tu’izzu man tashaaa’u wa tuzillu man tashaaa’u biyadikal khairu innaka ‘alaa kulli shai’in Qadeer
"Say, “O Allah, Owner of Sovereignty, You give sovereignty to whom You will and You take sovereignty away from whom You will. You honor whom You will and You humble whom You will. In Your hand is [all] good. Indeed, You are over all things competent." — (Qur'an 3:26)
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 3:102)
Allaahu waliyyul lazeena aamanoo yukhrijuhum minaz zulumaati ilan noori wallazeena kafarooo awliyaaa’uhumut Taaghootu yukhrijoonahum minan noori ilaz zulumaat; ulaaa’ika Ashaabun Naari hum feehaa khaalidoon (section 34)
"Allah is the ally of those who believe. He brings them out from darknesses into the light. And those who disbelieve – their allies are Taghut. They take them out of the light into darknesses. Those are the companions of the Fire; they will abide eternally therein." — (Qur'an 2:257)
The believer benefits from knowing that Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ is Al-Wali. He understands that real control comes from the commandments of whatever Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ wills. No one can dictate otherwise. It should further solidify the notion of reliance upon Him for all matters. He is the one who organizes the plan, puts it into action, and then preserves it. Shaykh Tosun Barak writes, "the whole of creation is governed by Allah's knowledge and power: not a leaf moves without His will. Neither is the movement of the leaf disconnected from other things moved by the same wind, by the same will."
So all matters are in the care of Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ, our being is part of a divine order He has planned. He is Al-Wali (The Ruler) and Al-Waliyy (The Protecting Associate). But one must realize that what may be good for you may not be in the way you want. Each caliphate asked Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ for wellbeing and protection, yet Umar Ibn Al-Khattab (ra) was martyred. Even Ali ibn Abi Talib (ra) was killed and martyred. Some may wonder about the justice in that, but the real reward is in the hereafter. The reward of one's actions is not necessarily manifested in this life. If it is, that is a blessing or a gift from Allah سُبْحَٰنَهُۥ وَتَعَٰلَىٰ, but it shouldn't be the primary motivation.
It was narrated that Sa'eed bin Zaid bin 'Amr bin Nufail said: "The Messenger of Allah was one of the Ten (given glad tidings of Paradise). He said: 'Abu Bakr will be in Paradise; 'Umar will be in Paradise; 'Uthman will be in Paradise; 'Ali will be in Paradise; Talhah will be in Paradise; Zubair will be in Paradise; Sa'd will be in Paradise; 'Abdur-Rahman will be in Paradise." He was asked: 'Who will be the ninth?' He said: 'I will.'" 
 Sahih (Darussalam) Sunan Ibn Majah 133 & Sunan Abi Dawud 4649