The vision of a global network of interconnected computer networks, which laid the foundation for the Internet of Things (IoT), was first proposed by "J.C.R. Licklider." His ideas and contributions to the development of the ARPANET, a precursor to the internet, were instrumental in shaping the concept of IoT.

CoAP (Constrained Application Protocol) is designed specifically for IoT scenarios where resources like memory and bandwidth are limited. It's a lightweight and efficient protocol that is well-suited for IoT devices with constrained capabilities. Unlike HTTP and TCP, CoAP is tailored for these resource-constrained environments.

A significant vulnerability in IoT devices is the use of weak or default passwords, which can be exploited by attackers to gain unauthorized access. It's essential to use strong, unique passwords to mitigate this risk.

IoT devices often generate diverse data types, including structured, semi-structured, and unstructured data. NoSQL databases are a suitable choice because they can handle various data types, provide flexibility, and scale horizontally to accommodate the growing data from wearable devices.

Requiring both a password and a biometric scan is a form of Two-Factor Authentication (2FA). It adds an extra layer of security beyond a simple password, making it harder for unauthorized users to gain access.

Advanced visualization tools in IoT are crucial for gaining insights from complex data. With the enormous volume of data generated by IoT devices, visualizations help in presenting the data in a comprehensible manner. This is vital for analyzing trends, anomalies, and making informed decisions in IoT applications.

Blockchain enhances IoT security through data immutability. Blockchain's distributed ledger ensures that once data is recorded, it cannot be altered, making it ideal for securing the integrity of IoT data, such as sensor readings and device logs.

Devices connected via the Thread wireless protocol are known for their ability to create self-healing mesh networks and connect directly with one another. Thread allows devices to communicate in a decentralized manner, eliminating the need for a central hub or router.

Requiring unique digital certificates for each device emphasizes Identity and Authentication. It ensures that each device is who it claims to be, adding a layer of security to prevent unauthorized access or data breaches.

The Constrained Application Protocol (CoAP) is specifically designed for IoT scenarios where resources, code footprint, and bandwidth are limited. It's a lightweight protocol that enables efficient communication between IoT devices and applications. CoAP is designed for constrained networks and devices.