A go-to guy is someone who has a lot of experience or knowledge on a particular topic, or someone who is especially reliable. This makes him the person to see if a problem arises regarding their area of specialty, or someone colleagues and friends can count on when in a tight spot. It may also refer to a person, usually a male who has a lot going on at any given time, making him the "go-to guy” when his friends are bored or need somewhere to hang out.
Traditionally, a go-to guy is someone who knows a lot about something in particular. For instance, if Jim is great at working on vehicles, he may become known as the “go-to guy” amongst his friends when they are having car trouble. This person is also usually helpful and willing to share his knowledge, making him very approachable. A go-to person doesn't necessary have to use his or her skills as a profession.
The phrase may also refer to someone who is not necessarily a specialist in anything in particular, but one who is always available to help when needed. This is generally a close friend who is admired, respected, and loved by those around him. He is often the first to help out in times of crisis or to lend an ear when a friend needs someone to talk to.
Often, a go-to guy is given such a title amongst a group of friends, but sometimes this can include those working in a professional capacity. He may also be someone a group doesn't know on a social basis, but someone whom the group mutually likes and trusts in his area of expertise. For instance, if everyone within a certain group use the same plumber because he is trustworthy and performs good work, he becomes their go-to guy, even though they do not know him well as a person.
A man can also claim this title at work amongst his superiors and coworkers. Someone who takes on extra work or consistently hands in superior quality projects may become his boss's go to guy when new assignments come up. This person may also become a well-known specialist within his field.
Less commonly, a go-to guy is someone within a group of friends who always has a lot going on. This typically makes him the “fun” one of the group, or someone others can count on for a good time. In this case, this person often throws a lot of parties or has connections to fun places to go around town.