Domain Name Resolvers
Domain Name Resolvers, also called DNS resolvers, are the computers which are used by ISPs to respond to a user request to resolve a domain name. "Resolving a domain name" refers to the translation of a domain name into an IP Address.
Simply put, the domain name resolvers cache the data and information received from users by means of queries. These resolvers are strategically located with ISPs or institutional networks and their main purpose is to respond to the user's requests related to domain names problems. These resolvers are used to resolve domain name related issues, which generally involves finding the corresponding IP Address.
In order to reach ICANN, the domain name resolvers first decode the request. In this way, the request is first processed by the resolver and split into its component parts. Then, the resolver will forward the request to ICANN in order to find the corresponding IP Address. The reply is forwarded to the user's computer.
Some consider domain name resolvers a waste of time given that it would be easier to directly contact ICANN; but the resolvers maintain a high level of performance, and are essential given that it would be very difficult for the root servers to handle billions of requests on a daily basis. 
ICANN and Domain Name Resolvers
The mission of ICANN is to ensure protection and preservation of the stability, utility and integrity the of DNS (Domain Name System). Some alternate root operators persuade other users to have their resolvers "point" to their alternate root (which is similar to the unique authoritative root of ICANN) instead of the authoritative root. Due to the fact that pseudo-TLDs are not included and recognized by the authoritative root of ICANN, these cannot be resolved by a large number of Internet users.
ICANN and the Authoritative Root
In 2001, ICANN released a policy regarding its commitment to a single authoritative root for the DNS as well as to the management of the authoritative root based on the policies created in accordance with the community processes.
There are many cases when organizations have set DBS roots as alternative roots instead of authoritative roots. Some of these alternate roots are purely experimental or operate within the norms established by the community but their common disadvantage is that these alternate roots have not been launched via consensus based ICANN processes and are not managed by IANA.
The DNS works based on a hierarchy. In this way, when a resolver is looking for information concerning a domain name, such as "www.icannwiki.org", it will be given access to the resource record about ".org" by one of the root servers, which informs the resolver which computers have authoritative information about the names within the .org TLD. The resolver then sends a query to one of those authoritative ".org" nameservers asking for details regarding "icannwiki.org". A query will eventually reveal thh IP address of the computer designated by the name "www.icanwiki.org".